I've been running it for about a month now, I've had no problems with it at all. It is MUCH improved over Tiger for handling Windows machines on the network. Previously you had to double click network, then your machine, then login and check the "Remember in Keychain" box even though it never would (this happens in 10.3 and 10.4). Now in Leopard you already have your network computers visible in the left pane (no double clicking network), then a single click to them connects you (no more logging in after the first time, even after restarts).
Other than that it seems about the same as Tiger. Although TimeMachine is pretty slick, just got that set up a couple days ago.