MailTags has received some attention at TUAW. If you're already a fan, you'll be very excited about the MailTags 2.2 Public Beta 3 that was released today. If you're not a current user, this might be a great time to check out a plugin that improves on Mail.app by allowing comments, tags, projects and other metadata to be attached to any message (among other perks).
Version 2.2pb3 introduces "MailTags Extras", which appears to be a plugin architecture for MailTags. It comes bundled with a first round of these extras, which include functionality for iCal Events and Todos and a quick way to color messages with a swatch palette in the sidebar. And as extras, these features can be individually disabled or uninstalled. Throw in some fixes for things like tagging issues, working with preferences and conflicts with other plugins and this is a release worth talking about.
With a final release scheduled for this month, this beta is maturing an already great plugin. MailTags 2.2 (Leopard) will be a free upgrade for registered 2.0 and 2.1 users, and the beta is available now.