I bit the bullet the other day and picked up my very own copy of OS 10.6 Snow Leopard.
First of all, despite what Apple initially said, you can get the cheap ($29.99USD/$34.99CDN) upgrade and install it directly over OS 10.4. You don't need to upgrade to 10.5 first, or buy the "box set."
So, with a quiet prayer for all my vital data, I slipped the new disk into my 2006 iMac, and hit "install." Right off the bat, Snow Leopard seems to be an improvement. Just the installation process seemed to go much faster than previous versions, taking about an hour and a quarter from start to finish, including updates post-install.
Second, Apple claimed you would regain at least 6GB of hard drive space (on your system disk) after installation, and they were being conservative. I gained 11.3GB, going from 165.55GB free to 176.85GB. That in itself will be worth something to anyone who can go through bytes as fast as I can.
Once all the updates are installed, the system also boots noticeably faster, in the 45-60 second range, down from about 75-90 seconds in 10.4. Shutdown time also seems to be shorter, but not as significantly.
Visually Snow Leopard is very similar to Leopard, so anyone using 10.5 will feel right at home, though those coming from 10.4 will notice some differences. Coverflow is available in the finder, and appears much smoother than it was in 10.5. Stacks are now much more usable, since you can navigate through folders inside them. Overall, the system generally feels "snappier." Folders and menus seem to open and close more quickly, most programs (especially Apple ones) feel more responsive in general.
Safari 4 may actually replace Firefox 3.5 as my default browser, that's how sweet it is. Again, Apple seems to have gone for something with a "snappier" feel, I don't know the actual numbers, but Safari now just
feels faster. Also if an individual tab crashes in Safari 4, only that tab is affected, the rest carry on their merry ways.
A few minor gripes: since the upgrade, I've been having some minor problems with Pages 2.0.2 and Word 2004. Pages crashes whenever I try to open a Word '04 document, and Word '04 takes forever to open. Also, you'll be prompted to download a patch before Word will open, and it won't open without that patch.
Well, I'll update this as I use the system more, but so far it looks like upgrading to 10.6 breathed a little extra life into a (recently out-of-warranty) machine. Is it a complete system-makeover that will dazzle you with shiny new features? Not on the surface (the experts tell me it's really quite different from 10.5 under the skin), but it feels a little bit better in pretty much every way. So, if you're using an Intel-based Mac, and don't have the cash (or credit) for a hardware upgrade, it is absolutely worth it to upgrade to Snow Leopard. It won't take all the age off of your computer (or its measly 1GB of RAM), but it will make it feel a little bit better.