There was a recent Channel9 video that confirmed the keynotes will be streamed live, and each session will be posted online within 24 hours. I thought there was additional confirmation of this on the official PDC blog, but I could be wrong.

There was a comment from Jeff Sanquist on Long Zheng's blog at http://www.istartedsomething.com/20081016/pdc-2008-sessions-scheduler-live/ "For those following at home we’ll have lots of great content for you. - You will be able to watch day one and two keynotes via http://www.MicrosoftPDC.com (lean back experience) and they all will be available on demand via Channel 9 in about 24 hours. - We’ll strive to have the individual sessions online on Channel 9 (http://channel9.msdn.com) within 24 hours. You’ll use the timeline view mention above in Long’s post to browse the sessions and each one will link back to a page on Channel 9. - The homepage of Channel 9 will be alive with behind the scenes videos (think directors cut of the PDC) for all the key stuff where go deep, connect the dots and show the demos too. Should be fun to watch at home."