IPB has this interesting feature that shows you an image on the first page when you login.
If there is a new version available, you see a 'there is an update available'...
If not, u see a 'you have the latest version available'...
this ofcourse applies to final versions not CVSs
Yeah, PopFile has that too, it would be really easy to implement, and it's a great help for those who want to stay current, but can't be bothered with checking websites ...
Of course, you could sign up at SourceForge and ask to be notified of new releases
I am subscribed to the WordPress Announcements (look below). But I am yet to recieve any mail from it!
I do send out emails to the WordPress announcement list whenever there's a release, but there hasn't been since October. You can also sign up for the bleeding edge list on the download page. That list is notified whenever there is a alpha or beta release. There will probably be an alpha release of 1.0 soon.