After a few days of letting my script make rounds through the GMail community, I can tell you that an unexpected number of people have been downloading it. That is great, but it also made me realize I'm amongst a giant group who finds the popup window irritating and that something should be done about it.
I tried contacting several people at Google to see if they would listen to me about the problem. After spending way too much time trying to talk to someone about it, I have given up. I'm sure the seriousness of this problem has not gone unnoticed based on the number of complaints they are likely receiving.
For now, thanks to Jonathan Feinberg, I have updated my original greasemonkey script to make it more specific to the offending popup rather than a blanket removal of "onmouseover" events -- this should prevent any future functionality from being automatically disabled. Thanks to everyone who has sent their gratitude -- it's my pleasure. I will try and make it a goal of mine to post fixes to the small annoyances that can be easily fixed with a little grease. If you have any suggestions feel free to leave comment or send an email.
Here is the updated script for anybody interested:
// @name GMail Popup Disabler
// @description Disable the annoying GMail Talk popup.
// @include http://mail.google.com/*
// @include https://mail.google.com/*
var t = event.relatedTarget;
if (t && t.tagName == 'TD' && (t.parentNode.getAttribute('class') == 'rr' || t.parentNode.getAttribute('class') == 'ur'))