This year though to try and make tickets sales more even, Apple is inviting developers to register to be part of a lottery.
"The opportunity to buy tickets to WWDC 2014 will be offered by random selection. Register by Monday, April 7 at 10:00 a.m. PDT for your chance to attend. We will let you know your status by email on Monday, April 7 at 5:00 p.m. PDT."
Apple will almost certainly introduce iOS 8 and I think a fresh UI for OSX but as for what else - let the speculation begin!