I signed up to attend the WWDC this year back in March. I'm certainly glad I did as it appears that WWDC has actually sold out (http://www.macworld.com/article/133468/2008/05/wwdcsoldout.html).
Makes one wonder if there will be a market for scalping WWDC tickets.
So far, I've attended two previous WWDC's: 2005 and 2007. The 2005 WWDC was pretty good and manageable with about 3,000 attendees. Last year, however, it was a bit crowded with closer to 5,000 people. It will be interesting to see what numbers "sold out" will translate into. Seriously, Apple needs to consider splitting the WWDC up into multiple conferences for the different areas (i.e. iPhone, IT, and Dev).
And the hotel rates!!! Wow have they gone up since last year! Last year I settled on the Parc 55 at $190US / night. This year I had to scramble to get a hotel for about $340US / night. I'm in a bit of sticker shock on that one. After a bit of investigation, I found that the WWDC is overlapping a diabetes scientific conference by two days (Monday and Tuesday) and for those two days, hotel rates are way up. Way to go Apple.