It's not world shattering like many users were unreasonably expecting. OTOH, it's only $29.
I didn't do a fresh install, just popped the disk in and came back an hour later -- good to go.
I do see an improvement on boot time, and faster opening of Photoshop and Microsoft Office suite. It's evolutionary. An overall improvement. I haven't seen any upgrade issues or problems, except my main photo-editing software doesn't work with it. That company (Nikon) isn't known for software excellence, especially for Macs, so I wasn't surprised, nor was I upset.
One thing I did notice was the number of updates to existing programs I had that came out more-or-less at the same time. Far more than I saw with the upgrade to Leopard, so it seems to me that developers were more proactive this time around, or Apple did a better job of getting them in the loop, or the necessary tweaks weren't as big a deal Leopard-to-Snow Leopard as they were from Tiger-to-Leopard.