I have to clarify, that peoples experiences with CM9 have been generally positive across all devices, as it can make the less powerful devices a fair bit more responsive. But since I find touchwiz and the default ROM for the GSII is actually not that bad (just a little bloated), I'm staying put. My advice is to Root your device and put a new launcher on it to begin with (like GO Launcher, if it takes your fancy), if you still demand more out of your device, and want to try different things, then there isn't much hurt in trying CM9/10 for a bit, and seeing how you get along with it.