Among the changes Leopard introduces is that unless you
enable "Bluetooth Sharing" in the Sharing preferences panel, any attempt to send files to your Mac via BT fail. For me, this is a critical part of my GTD work flow, of voice memos from my mobile phone being transfered to my Mac for processing this way.
Outgoing transfers, which I hardly use, seemed to work regardless of
this setting.
Too bad Apple doesn't bring up some informative error message on such attempts and had me waste quite some time figuring this out :-(