Eye candy yes, useful no.
#1 On the first reboot of Leopard it managed to not find one of my disks. Later reboots found it though.
#2 The keychain is not propagated correctly.
#3 Lots of stuff breaks like PGP in email. Of course, you manually have to move your old keychain over to use email since the keychain is renamed. Perhaps changing the name might work. I couldn't be bothered.
#4 Telling it to restart takes an act of God. It thinks it is busy with time machine or something. Time machine might be useful, but not if it gets in the way of shutting down or re-booting.
Yes this is being written on my old Panther system. I would not bother to "upgrade" to this system for a while. Its still in beta. Actually I think its rather in worse.