Google Notebook and Google Bookmarks were affected to Cross Site Scripting vulnerabilities, information was posted to well known Bugtraq security mailing list today:
securityfocus.com/archive/1/49 ...

And these security issues are reported as fixed by Google

This kind of vulnerabilities only work(ed) if you agree to install a widget/gadget or add a note in your Google Notebook from a unknown people.

The real vulnerability is not in Google's tools, it's in USER...