Having been a Leopard user for about a week now, my impressions of it basically echo what Rand has to say. I've not yet used Time Machine - heck, call me old-fashioned but I still think wireless networking is a pretty neat idea, so the laptop hasn't been in one place long enough for Time Machine to get acquainted with an external drive.
Have had a few niggles here and there, Apple's (pre Time-Machine!) Backup utility is completely refusing to restore anything I had backed up to .mac with my Mac Mini, but there was nothing terribly important so, in the words of Catherine Tate, I Ain't Bovvered.
One thing that I have found useful (to my surprise) is the Notes feature of Mail. I am one of those strange people who emails themselves on occasion - adding a Note makes the process much more, I dunno, less strange, and more useful.
But, as per Rand's review, my impressions are also overwhelmingly positive. I think we'll be very happy together :)