I have said before that Mozilla Thunderbird needs a "Purge" button equivalent to that in Outlook Express. In the time since, I have been using Thunderbird despite saying that I'd stay away until a "Purge" button is implemented. Why? I guess because it didn't seem like a Purge button was going to be implemented anytime soon (and also because of increased security and protection from OE-targeted worms and viruses).
A commentor reminded me about the existence of an extension that gives you a "Purge" button. I say "reminded" because I'd seen this extension before in the MozillaZine forums way back in the early months of this year. Somehow I forgot all about it since then and have been frantically right-clicking on each folder and selecting "Compact This folder". Which kinda sucked because that's a whole lot of clicking going on especially with multiple accounts. Now I can do the same with just 1 click (per folder).
And couple that with the Buttons! extension, it's so much easier to get rid of junk mail. 2 clicks and junk mail is purged. These buttons really should be in Thunderbird itself.