Snow Leopard was received in the post on the 29th and quickly installed. I say quickly; it took a little less than an hour to upgrade my machine though I am assured a fresh install takes less than 10 minutes.
No unexpected problems after the install: iStat menus don't work, neither does PlugSuit. iStat I was surprised about but PlugSuit is a hack which, had I thought about it, would have been sure it would fail.
First impressions? Exactly the same as for Leopard 10.5: "is that it?"
The only really obvious improvement is Mail, which is now blindingly fast. Seriously, it's nearly as quick as Thor on the Amiga. The problem here is that gpgMail has failed again. When will Apple give us a stable API to add these features in? PGP / GPG is essential!
Expose is better. Spotlight seems quicker, but I've not tested in detail as I've had little use of it yet. In general, the whole machine does seem quicker overall. I really don't think I've had any pauses or waits for something to react while using 10.6 today, in situations where 10.5 would leave me waiting for Finder to open a directory or crawl through for preview thumbnails.
I expect Snow Leopard to mature over the coming months as software is released and upgraded to take advantage of the revamped internals. I really do feel the same about 10.6 as I did for 10.5 (in that I couldn't see the need to upgrade from 10.4) but as 10.5 matured and realised its potential I found Tiger to be less and less attractive.