Well that was quick! WWDC 2012 finished on Friday and here we are on Wednesday with the sessions videos available for download. Assuming you are an Apple registered developer (iOS or Mac) you can download the videos from developer.apple.com/videos/wwdc/2012/.
It easy to overlook but there is also a separate disk image containing all of the WWDC 2012 Sample Code.
As for WWDC 2011 the videos are available in both HD or SD formats and with only a few exceptions include the accompanying slide deck. There are over 100 videos and for sure I will not watch them all but I expect to work my through many of them in the next couple of months.