Hi, Rudy—
I have ~/Library/Mail/Bundles/GrowlMail.mailbundle and that directory seems in proper oder.
My version of Mail.app is the same as yours: v5.1 (1251/1251.1)—I apologize for the typo.
The patcher showed that I had two versions of Growl Mail.mailbundle: one in ~/Library/Mail/Bundles/ and one in /Library/Mail/Bundles/. I removed the latter, uninstalled, and reinstalled. No joy (even after restarting).
The GrowlMailUUIDPatcher indicates that everything is in order and sees nothing to do.
Note: when I first ran the installer, it indicated that Growl Mail would be installed for all users, though it only put the GrowlMail.mailbundle in ~/Library/Mail/Bundles/. This notice did not appear when I ran it a second time (over the previous installation).
Alan