I don‘t know about you, but I have found that I use Keychain a huge amount. I use it to store passwords (obviously), notes (using the secure notes feature), and serial numbers (again secure notes). In Tiger, Apple have really made the whole application a lot more user friendly with separate panes in the window for different keychains, and for keychain item categories. The latter of these is the real usability bonus, allowing you to see just notes, just internet password, just application passwords and so on. Now all of this functionality might have been there in the Panther version but it certainly wasn’t well laid out.

Finally it's worth pointing out that with the Quicksilver Keychain plugin, all of the keychain items are available instantly from within QS - very handy for when Safari forgets that it has a password stored!

All in all a nice improvement!