Tonight is the beginning of Shavuot.
Shavuot celebrates the day that G-d gave the Torah to the Jewish people. It's also a harvest festival, signaling the end of the barley harvest and the beginning of the wheat harvest. It's traditional to stay up all night (what's known as a tikkun) studying Torah, Talmud, and other writings. Then at sunrise, you do a really early morning service.
There's also a tradition to eat dairy, possibly stemming from the notion that Torah will be to our hearts as milk and honey are to our tongues. So, cheese blintzes, cheesecake, ice cream? Bring it on!
There's some more info here from Judaism 101. And I've also referenced Jewish Literacy by Rabbi Joseph Telushkin.
Gotta run! Chag Sameach (happy holiday) to all observing!
(And feel free to correct me if I've gotten my information wrong.)