Whether or not the personal privacy concerns about Google's webmail have merits, browsers should feel that their privacy is being severely infringed upon! Google uses some very unusual techniques to gather large-scale test results on browser compatibility as a part of their beta testing.
A part of their script is a function called DB_SendJSReport. Throughout their code they have embedded checks to see whether the browser behaves as expected, or whether it complains about an error. They catch any error complaints from the browser, any unexpected events and — send off a report. It includes the complete UserAgent string to identify your browser in complete detail, the text of the exception or a plain English description from the Google team of what the event they checked was, what version of the GMail libraries was used – and it even includes your GMail E-mail address. (Actually, they might be able to tell that I have been snooping around in their code and changed bits and pieces for debug purposes, but I really doubt they can be bothered tracking THAT, even if it in theory may be against their user agreement..)
We'll see if it pays off in terms of browser compatibility – I'm quite sure it will. For instance, Opera had problems with Yahoo's menu for ages. If Yahoo had had such a problem-tracking/debug system they could easily have added a check to see if the offsets where the menu was shown seemed sensible, and test with the browser and fix the script if there was a relatively significant irregularity.
Now, we'll just try hard to get that GMail compatible Opera-release out! 😎