Grab with both hands and run but if you want to spend anything on it after purchase, upping it to a gig of RAM would oil the wheels perceptibly, especially with Leopard.
But I'd grab one for 50, its a decent Mac, and its very different from anything Apple has now, its great for college, no one would steal one of those(when their are laptops everywhere)
I am starting to think it depends on system config. My PB G4 1GHz is slow as molasses in leopard. However my wife's ibook G4 1.42GHz is very snappy. Difference other than processor is iBook has "core image accelerated". (See Sig)