It is implemented. As long as your browser supports showing title="..." contents (IE 5.5+, Netscape 6.x, Mozilla all do), then you'll message preview show when you hold your mouse cursor over the subject. You can change this to be a javascript (eg. overlib) easily by modifying the templates (It's just a template variable).

The size of this message preview is user definable (0 - 500 in length). The default should be set to 100 in length for the message preview. If you've signed up for an account on freemail.gossamer-threads.com/mywebmail.gossamer-threads.com before the 2.1 update, then your default will be 0. Just go into Options => Display => Message preview length. The option only shows up on the "brewt" and "nessa" templates though.

There's a few new features on the user side you should take note of:
1) Of course, the message preview
2) Empty Trash button (in Trash folder)
3) Send deleted mail to Trash (Options => Mailbox)
4) Empty Trash on logout (Options => Mailbox)
5) Show message source (Message => Header => Show Full Message Source)
6) Send email to people in Address book from the Address book page (Select their name, and click Send Email)
7) Improved Help pages
8) Many people wanted the quota to be reported on the main page... you got it
8) Many other smaller bug fixes

Adrian