Rated 2 out of 5 stars
This extension is really powerful, it should be a "must-have" for all power users of Thunderbird.
I can however not recommend this plugin just yet due to serious bugs
Do a quick search using GMail-UI, press CTRL-ENTER to create a global search filter. Search finishes of fine, but now normal quick search in GMailUI will not function until Thunderbird is restarted. Pretty anoying. The error seems to be for all platforms, Windows as well as Linux.
I would rate this extension 5+ if it in fact did not prove that it actually does not work as intended (even in 0.6, I have been running 0.5)