Interesting. We run Suitcase on a few Macs here (couple of dual G4s and one Dual G5) and it runs decent. A bit of a delay when activating fonts, but not too bad. Guess it's all relative. Could definitely be zippier though.
What really sucks though is that I've waited for quite a while for Extensis to fix the autoactivation to work with CS2. They finally got that going recently and now it's broke again (either because of the latest Tiger update or the CS2 update, I'm not sure which yet).
I'm convinced Extensis is primed to release an updated font manager for a couple of reasons. 1, they bought Font Reserve quite a while ago (well over a year ago I believe). Presumably they bought that to acquire technology, it's utterly stupid for the same company to sell essentially the same product, which is what they've been doing for a while now. 2, Extensis recently announced deals on Suitcase. My guess is they're urging a selloff (my like Apple does) prior to an update.
It's a long time coming. Overall, I still prefer Suitcase in spite of its flaws. I've tried them all (and I mean all of them) and I still prefer Suitcase's multi-font preview and general interface. It also handles boatloads of fonts better (even if actually activating them may be a bit sluggish).