I've been test driving the Google Sidebar for a few days.
It is interesting from the standpoint that it has a pluggable architecture with available API's (Brad thinks this is good :-)) The "out of the box" Sidebar items are fairly vanilla and include widgets like weather, news, etc. Several of the widgets, including "Quick View" and "Web Clips", sniff IP traffic to monitor sites you have visited and RSS Feeds among other things.
The Quick View widget works pretty well for IE traffic, however, for some reason it refuses to monitor anything I visit in Firefox. The Sidebar image shows Firefox views, so it must be me. Anyone encountering a similar issue?