According to http://gigaom.com/apple/wwdc-2011-sells-out-in-less-than-one-day/ "...

According to http://gigaom.com/apple/wwdc-2011-sells-out-in-less-than-one... "WWDC 2010 took eight days to sell out entirely". That's pretty impressive assuming the same number of tickets (5000) were sold.

http://en.wikipedia.org/wiki/Apple_Worldwide_Developers_Conf... mentions the number of tickets being capped at 5000 for the past 2 years.