I installed OS 9 and found the new features to be a benefit for the most part. My PB 3400c 80MB RAM ran okay...but I was taking a performance hit someplace. I looked all over and finally found a "checklist" in the MacOS Help. Recommended tuning the mouse, keyboard, trackpad, and turning off VM. With VM "on", the Finder was using about 18 MB of RAM. With VM "off", it jumped to 30 MB +. This made my performance jump through the roof. I could not be happier...but the whole jump from 18 to 30 MB of RAM is not very pleasing.
Guess I will have to max out my RAM in the Powerbook. In all, a very cool operating system.