VLC. I'm not totally sure if this will work for everyone or if it just was generated for me, but this is the rtsp address it uses (and it works in VLC for me).

rtsp://a2047.v1413b.c1413.g.vq.akamaistream.net/5/2047/1413/1_h264_110/1a1a1ae656c632970267e04ebd3196c428970e7ce857b81c4aab1677e445aedc3fae1b4a7bafe013/11piunpaiubsdvadibvas06_1_220.mov

Maybe playing this link will work?

http://stream.qtv.apple.com/events/jun/11piubpwiqubf06/11piu...

After a few days there is usually an mp4 file of the keynote published on the podcast feed for the Apple Keynotes. Someone will usually share the link then.

So much for the open web.