Ya, I have tried it, back when it used Keychain, but not Safari's keychains. I think they integrated it, but the cost of the application, and the fact FF3's password manager has been recoded to allow easier integration with any OS's version of Keychain, makes me not want to buy 1password, and wait for either a plugin, add-on, or native FF3 integration.
I believe FF uses OS X's dictionary now too, that was another reason to stick with Safari, I have many acronyms that I have added to the dictionary, and do not want to add them again. The Keychain is the main factor though. I will wait.
I just moved from Mutt to Thunderbird as a trial, to see if I like it. So far not bad, but I have specific IMAP requirements. I need not just IDLE but IMAPENHANCED_IDLE. It seems to have it down, but its hard to tell if its looking in each directory, or actually listening to the IMAP connection.
Back on topic.
FF3 is a good browser, but not necessarily better than Safari (with Saft and inquisitor) but that is my opinion.