Lots of customs and traditions have been developed for it, though. (Like much in Judaism, there are multiple reasons for most of these. And, in this case, there's generally no way to know which is the "right" or "original" source of these customs. They're just part of the holiday now, for several reasons, and that's enough.) For one thing, Shavuot is considered to be the anniversary of the giving of the Torah on Mount Sinai. That's reason enough to enjoy the holiday. We read the Ten Sayings (commonly mis-referred to as the Ten Commandments) in synagogue! It's fun!
It's also become tradition to eat dairy-laden meals all holiday long. (Some people don't have any meat all holiday long, but that probably wasn't originally part of the tradition, and anyway, lots of my friends don't eat meat the rest of the time either.) Also fun! I like good vegetarian food! And blintzes! Unlike on Shabbat, cooking is permitted on holidays, so I made myself scrambled eggs with cheese for lunch. The rest of the year, I tend to be too lazy to do something like that.
Because of the connection to the Torah, Shavuot has turned into a learning holiday. An old tradition, resurrected in the past 40 or so years, is the all-night Shavuot study session, "Tikkun leil Shavuot". This explains why I was talking to my rabbi so late last night. After services ended at about 8:30pm yesterday, a bunch of us stuck around to eat blintzes and study together. We talked about the nature of Shavuot, the connection between prayer and song, prayer and Judaism as performative acts, and so on. It's nice to be able to discuss this stuff in an environment where going off on tangents isn't discouraged. After all, we have all night to finish!
At about 12:30am, we were an hour into some mussar text that the rabbi used as an appendix in his recent book. I was having trouble keeping up with the discussion, because at that hour, either it was too dense for me or I was too dense for it. (And besides, I'm sure I wasn't the only one there who didn't nod knowingly when someone said, without explanation, that a particular passage seemed to evoke Adam Smith or John Locke.) I wasn't tired yet, but I decided that this wasn't my kind of philosophy. So I bid farewell to the 19 remaining people, went home, and read some Feynman until 2. Apparently, some of my friends stayed until the end of the session at 1:30, and then undertook the 40-minute walk to Penn and actually did keep studying until sunrise. I would've gone with them, but I needed a change of pace sooner than that.
In recent years I've decided to expand on the studying theme, and use the holiday as an opportunity to read some books that are a bit more in-depth than my usual fare. Shavuot is a very mystical, Kabbalistic holiday in many ways, not the least of which is the choice of Ezekiel chapter 1, one of the foremost Kabbalistic source texts and some pretty trippy stuff, as the haftarah reading (standardized selection from the books of Prophets, read publicly in synagogue) for the first morning of the holiday. To that end, in each of the past two years, I read one of Mitch's two books, both Kabbalistic novels, in its entirely during the holiday. (Real Kabbalah, not the Madonna pseudo-neo-pop-Kabbalah.) Unfortunately, Mitch's third manuscript has not yet been published (may it be built bimheirah b'yameinu), so I couldn't continue that tradition this year. Instead, I read some Feynman and some Hawking, and finished up with a rereading of a couple selections from Mitch. I had interesting beginnings of thoughts comparing the emptiness of pre-Big-Bang space, the emptiness commandment-wise of this holiday, and the world of atzilut. Unfortunately, I don't know enough about any of these concepts to really explain further. Must read more.
Anyway. I decided to keep only one day of Shavuot this year, whereas most of the major Jewish holidays are traditionally kept for two days by non-Reform non-Israeli Jews not currently in Israel. I'm sure that BZ (mahrabu) will soon post a much more thorough explanation of why he only keeps one day, and many of his reasons will apply to me too. (In large part because he's one of my main influences in terms of Jewish practice.) But I learned a lot about this sort of stuff this year, when studying Rambam's hilchot kiddush hachodesh (Maimonides' codification of laws regarding the sanctification of the month; a volume of his Mishneh Torah) with a friend, and therefore drew my own conclusions. My reasoning is as follows:
The reason most 2-day holidays are 2 days in the diaspora (beginning and end of Pesach, beginning of Sukkot, Shemini Atzeret which falls at the end of Sukkot, and Shavuot, but not exactly Rosh Hashanah) dates back to the period of the rabbis. In olden times, it was up to a religious court in Jerusalem, rather than a standardized calendar, to determine every month when the new moon, and therefore the new month, had officially started. After this determination was made, messengers were sent out (in most months) to alert the populace of the exact date of the new month. This was important information if a holiday was due to begin on the 15th of the month, such as Sukkot or Pesach. Since the messengers only had 11 or 12 days to travel before the 15th (can't travel on Shabbat or Yom Kippur!), word could only travel so far in time. It was decided that anyone outside Israel couldn't count on hearing in time, and should keep both of the possible days of these holidays (based on the two possible days for the new moon, since a lunar month can only be either 29 or 30 days), since they didn't know for sure which one was the "real" one. Even if the messengers arrived in time once, one should still keep two days, in order to be consistent.
Alright. That justification is a bit shaky now with the standard calendar, but it's enough for me. A lot of laws in Judaism are based on rationales that don't apply anymore, but the laws still stand. I haven't decided on a consistent approach for myself for all of these laws, but in general I keep a lot of them.
The problem here is that Shavuot isn't on a particular calendrical day. Shavuot falls on the 50th day after the first day of Pesach. It just so happens that that's been the 6th of Sivan every single year since the standardization of the calendar. But that's coincidence, not design. (The Torah doesn't specify a day.) In fact, I've literally been counting the days until Shavuot! (Third straight year without missing a day!) The formula for counting doesn't include an ambiguity based on when Pesach might have started. On the third day of Pesach, you don't say "Today is the first or second day of the Omer". I've been sure since the first seder exactly which day Shavuot would be this year. It seems absurd to hedge my bets now. Besides, the messengers for the new moon of Nisan, Pesach's month and therefore the new moon that determines when Shavuot will fall, would surely have gotten to the end of their journey by now. After all, they left over two months ago.
Rambam, by the way, seems to concede that the messenger problem doesn't apply to Shavuot. His reason for keeping a second day is that one shouldn't differentiate between the holidays, keeping two days of the others but one of this one. That reason just isn't good enough for me.
Nonetheless, I'm going to try to sort of keep the second day of the holiday, a little bit. I have off of work anyway, I might go to synagogue in the morning, and I have holiday lunch plans. I also won't do anything potentially stress-inducing, like driving. I'll read more, and not use IM. But it's not really a holiday for me now. And I think I like that. Shavuot doesn't seem focused enough over two days.
Tonight I went to shul, and I didn't daven mincha with the tzibur because it was too late in the evening for me (I had davenned it myself earlier), and I davenned ma'ariv l'chol when everyone else was doing Shavuot ma'ariv. It's remotely possible that I'm the only non-Israeli in the world who would go to shul this evening but do that. It's nice to be different.