My experiences are a little different - but then I started from a different place.
I got a new mac Pro in September last year and as I knew that Leopard was on the horizon, I only loaded up those apps that were essential to my work i.e. Appleworks, FMP6, CS3 and iWork 08.
No problems with the system at all.
My wife came back from the US the day after Leopard was launched and brought me a copy, and Aperture 1.5. (cheaper than buy them here!)
Did the upgrade and started playing. The only thing that I didn't really like was the translucent Dock and the almost invisible glowing balls. A few days later I found an app called TigerDock, and that got my old dock back.
The only problem I expereienced was with Safari. When I closed it, instead of closing it would always put up a message to the effect the "Safari has unexpectedly quit" - however, in every respect i appeared to have closed properly, history, cache & coockies all appeared to be correct. This behaviour still continues - even with all the latest updates.
Time machine has not given me any problems at all, it has been rock solid - working to an internal drive.
As you say, Quickview is a godsend - I only wish it would work on Appleworks files - I have thousands of Drawings created over the past 10 years. Annoyingly, iPhoto work won't work with AW drawings either. (whereas Extensis Portfolio on my old mac works with whatever I give it to catalogue). It doesn't work with IDD files either.
One thing that did surprise me, when using the coverflow concept for browing files, is that the icons have full transparency. That may have been in Tiger but I think it's new - possible this Quartz Composer thing (or whatever).
Here's a trivial something which I've discovered that many of my clients have not yet found, but really makes jaws drop. Go to the screensaver control and scroll down and select the pictures folder. On doing so 3 new buttons appear under the preview window. Pick the one on the right - that looks like a grid.
Activate the screen saver and wait.
It pays to have a well stocked iPhoto library.
I haven't done the latest security update yet, I'll wait a few more days and monitor the boards to see what's happening first.