I tend to be very conservative with software updates on my MacBook, as it is my main writing machine. But some software I wanted to run forced me to do the upgrade to the latest Mac OS X version. And a great update it is.
Snow Leopard brings 64-bit computing to the Mac core applications and a great performance boost it is too. Startup from cold or sleep is MUCH faster, as is shutdown or sleep at the other end. Things like Mail and Safari operate MUCH faster as well.
Interestingly, I have found my Mac generally much faster in all applications. Photoshop is faster to open up and opening files also seems noticeably faster, as are the other Creative Suite applications.
Now that 64-bit seems to be working well for the Apple core we can only hope that the soon to be announced CS5 includes 64-bit mode for the Mac, which was left out of CS4 because (according to Adobe) Apple had not sorted the 64-bit side out properly yet back when CS4 was rolling out. Given the apparent issues between Apple and Adobe over Flash and the iPad, I hope this does not impact on 64-bit for CS5. Many of us love both Apple and Adobe products and need them to play nicely with each other.