MailTags update: 2.2b5
At last I can feel comfortable about upgrading to Mac OS 10.5 Leopard: MailTags has a public beta for Mail.app 3.0. While the beta appears to be stable (hence its being made public), you should keep backups of your mailboxes. To-do and event capabilities have also been temporarily removed, as iCal interoperability has changed dramatically.
For a full description of what’s working and what’s not, see the 2.2b5 forum announcement.