Yeah yeah
OS 9.1 is a quick hack.
The full CD version is nice - but the UPGRADE is absolutely awful.
My system under 9.04 was as stable as anything out there, if not more so. After upgrading, I had constant system crashes, hard freezing, and there was a minimal slowdown.
The updater also caused drive corruption routinely. This is evident on may peoples systems.
After downgrading all of these problems went away.
My advice:
If you have 9.04, stick with it.
AVOID the updater like the plague.
If you have a full CD install, ok, fine, do it, but I still prefer 9.04.
One thing I liked about 9.1 is how it recognised the OSX packages and you could right click and "show package contents" - though thats not necessary in 9.04 (they're just folders).
Save yourself the trouble unless you wanna use Classic.