Existing users, 
Version 1.1.2 doesn't notify of incoming mails (Mail) nor completed downloads (Safari).
Hope that a Leopard compatible version will be out soon.
Growl
Allows apps that support Growl to send you notifications.
Version: 1.2
Waiting for a Leopard friendly version
Feedback Type: Review
Contributed by: Giorgio Boccalari Sunday, November 04 2007 @ 06:57 AM PST
Product Platform: MacOSX
Used Product For: Less than a month
Comments
Waiting for a Leopard friendly version - A. Henket
Even if this version were not to work on Leopard, which it does, it still the most Leopard friendly version to date. Give it a new try and after installation of GrowlMail, enter this in the Terminal, with Mail.app closed, to make sure:defaults write com.apple.mail BundleCompatibilityVersion -int 3
defaults write com.apple.mail EnableBundles -bool YES
Worked for me. The installer in later beta versions did not adjust these settings properly. Possibly this was not fixed after it was reported.
Sunday, November 04 2007 @ 11:41 AM PST
Waiting for a Leopard friendly version - TheSin
the Mail plugin works for me, well I wouldn't' say works if there is 1 or 2 emails that come in and my screen saver isn't on it works, other wise it displays them then locks mail up. So I wouldn't recommend using it but they are getting closer.Reply to This
Sunday, November 04 2007 @ 09:19 AM PST