WHEN IS IT?
The sixth of Sivan (late May or early June).
ANY SPECIAL OBSERVANCES?
Tikkun Lel Shavuot:
Sorry for those who aren't night owls but it is customary to stay up the entire night before Shavuot. Why? Well, there's a legend that the Jews at Sinai slept too well, that they should've been more eager. The Zohar says that one should stay up just like a groom stays up the night before his wedding because he is eager for the next day. I can hear the shocked gasps from some readers that I should mention the Zohar. Yes, the Zohar is a kabbalistic text. I'm not advocating all the teachings of Kabbala.
Eating a ton of dairy:
Everyone (except the Yemenites--they've always gotta be different--just kidding, I love you guys) eats dairy on Shavuot. Why? Because the Torah is milk and honey (Song of Songs 4:11) and also because if Passover was the "birth" of Israel then Israel was just a baby at Sinai. And we're all infants if you think about it (when it comes to Torah).
So I think Vilna Gaon was totally against this as a supposed Christian custom but it really isn't. Shavuot is an agricultural day let's not forget. And so decorating the home and synagogue with flowers and foliage is quite fitting in my opinion. Plus, a flower always brightens a room, don't you think? And we're supposed to enjoy Shavu'ot like a wedding day after all.
Reading the book of Ruth:
This custom goes way back (Masekhet Soferim 14:16). Why read the book of Ruth? Well, sorry to disappoint Boaz and the Exclusionist groups out there but Shavu'ot has some universal implications. The story of Ruth occurred at what time? The harvest! And so, in the latter days, the prophets say there will be a world-wide harvest, an in-gathering of not just Jews but also non-Jews! Take that Boaz! You can't stop G-d!
Here's some suggestions for songs to sing on this beautiful day: