The first "class" was 6/2005: Reddit (made it pretty big) Infogami (joined reddit, "made it big") Kiko (sold for ~$250k, started Justin.tv - likely to make it big) Loopt (well-funded, great traction, seems likely to make it pretty big) ClickFacts Firecrawl (one founder joined TextPayMe, another YC company that sold to Amazon) Simmery (one founder joined Reddit and presumably made it sorta big) Memamp
--> That's 50-75% seeming to have a pretty good shot at making it somewhat big.
You can head to: http://spreadsheets.google.com/ccc?key=0AkkhSN3vaY4jdF90b1l1...
and do your own math, but it's pretty premature for most of the classes.