I've found that NetBSD works better than linux. Seems faster...
Performance pretty much depends on your gear. An 060 is ok, but X is not usable unless you have a good gfx card. Even then though, performance is limited on Cirrus based cards (Picasso's II/IV + only 8bit color and no support for the onboard blitter). I've heard cybervisions are better, but havent used one myself.
I'd say it's a nice geek toy, and a place to learn about unix. They do run stable though, I had a PHP+SQL+Apache server running on an A1200/030 24/7 without a single crash (it was way slooooow, though).