This is the biggest day of the admission year. Many of us think of the year as "before May 1st" and "after May 1st". It's the National Candidate Reply Date. It's also notification day for transfer students.
First years with offers of admission, you have until 11:59 PM to log into the SIS, hit the accept button, and pay your deposit if you want to be part of next year's incoming class. Obviously, you can also hit the decline button and then answer a few questions about your application experience at UVa. First years on the waitlist, your "decline" buttons will still work after today. You can remove yourself from the waitlist at any point.
I just took at look at the transfer blog and one of the recent posts has over 200 comments on it! To think that I thought the first years were chatty! I'm kind of jealous. :)
Oh, by the way, The Washington Post did a nice article about Chinese students studying in the US and it features UVa pretty heavily. The slide show is especially nice.