From a few days of testing and regular use, Snow Leopard is fine. Noticeably faster, takes up less space on the drive, and plenty of pleasant surprises feature-wise. No important applications broke in the transition. Amazon now has it for $25. I might be annoyed if this was a $100 update but I’ve almost forgotten the $30 charge (with free overnight from Apple).
And, you don’t need 10.5 installed on your drive. I had 10.5 installed and the 10.6 disk tried to upgrade 10.5. I didn’t want that. I booted from the 10.6 DVD, wiped the drive and installed a fresh copy of 10.6 without incident.
And, there is a great new mountain wallpaper.