Read/WriteWeb's Web 2.0 Summit coverage sponsored by Yahoo!
Marissa Mayer from Google only has 10 minutes to speak at Web 2.0 Summit, so she gives a high level look at Google's use of Ajax in applications. She notes that the key reason they created Gmail in Ajax was speed. This is a theme in Google Maps too. In terms of Google Videos, she says how instant something is and giving instant gratification is key - they used to make users wait 24-48 hours to see their videos after uploading to GVideo.
In conclusion, she says speed is very important for web 2.0 and the future of the Web.