This article by Wayne Mery will show up in the next about:mozilla newsletter, and says it all:

Or more correctly, Thunderbird is putting bugs in the cross hairs. As part of it’s attention to users and quality, the reinvigorated Thunderbird team has announced weekly Thunderbird Bugdays. Bug day will be held every Thursday as part of a multi-pronged effort: 1) to reduce the number of bugs in the bugzilla database to a more manageable level – for both confirmed and unconfirmed bugs, 2) to respond to and assist bug reporters in a more timely manner, and 3) to improve the quality of the bugs in the database such that they are more easily acted upon by developers and volunteer hackers.

Bug day brings together seasoned Thunderbird users and users new to the bug process each week for a day of bug squishing/squashing/mashing/improvement. #bugday on IRC is the vehicle for veterans to help and mentor new participants. #bugday is also the collaboration tool that allows everyone can help each other, to gang up on bugs, and have fun.

The Thunderbird team needs your help to make bug days effective and fun, so please take a look at our planning document and add your thoughts to the wiki or post in the dev newsgroup.

To quote k5ehx from our second bugday, “Bug Squashing is fun!” To all Thunderbird enthusiasts, we look forward to your involvement.

Thanks Wayne and Gary for leading this great effort!