We have recently seen a small number of University computer users being denied Web access temporarily as a result of repeated unauthenticated requests made by the Google Earth application to Google's servers. This appears to be associated with the latest version of Google Earth, 5.2.1.1588, and in particular with the Tips and some of the map layers such as Panoramio.
We will be investigating this further to look for other solutions but if you are experiencing this problem it might be worth downgrading Google Earth to an earlier version.
Here are two posts on Google's own forums referring to this issue:
http://www.google.com/support/forum/p/eart...a15f9&hl=en
http://www.google.com/support/forum/p/eart...5b56d&hl=en