Apple released its session videos from WWDC and many people are having problems watching them. Apparently, Apple is limiting playback to Safari on the Mac. If you try to watch the videos on an alternative browser, even on a Mac machine, you receive the stern warning that "You need to use Safari on the Mac to view this video.
We have no idea why Apple has this policy. Both the keynote and session videos are encoded in H.264 so they're in a format supported by a variety of platforms. The easiest workaround for this problem though is iTunes. All these videos can be watched from the media software without worrying about which OS or browser you are using.