The Pew Internet and American Life Project is an excellent resource for those people looking for confirmation that Web 2.0 technologies and behaviors have fundamentally changed the way we communicate.  A recent report shows that 48% of people surveyed had visited YouTube or similar video-sharing sites in the past year verus only 33% of people surveyed last year who had engaged in such behavior.  

Certainly the challenge in public relations is how best to weigh the significance of these findings.  Perhaps people are not yet watching YouTube the way that they watch CBS, but the important thing to realize is that they are becoming increasingly comfortable with the medium.