I just upgraded to OSX Snow Leopard on my 13" aluminum MacBook. My Mac leapt to life.
First off, the gamma was changed a little to give a better color that people were wanting. It freed up around 10 gigabytes on my hard drive. The core is excellent as well. Programs just open. About 1/2 second to open Safari 4. I'll post more when I'm done thoroughly looking through it.