I don't have any hard evidence to back this up, but I think it's around 15% I've heard both 10 and 20 from different sources, so somewhere in between makes sense.
Someone else on here probably has a better idea than I do though.
About 10% of deferees or so are accepted. Of course, these are generally the people who have above average stats than the rest of the deferees, and continue to show improvement by getting good grades in their first semester of senior year.
I guess 10-15% sounds about right since regular admission is around 33%? I guess I better keep up my grades! Thanks for the input guys, hopefully I'll see you all at U.Va. in the coming fall. Go cavs!