If you get it for like 300 bucks or less -- I wouldn't pay more than 250 personally for one -- stuff it with a 512k ram chip and it should do well with Tiger.
Whatever. I ran 10.2.8 on a 315mhz overclocked beige powermac. With only 224mb ram and it was fine. Not AMAZING, but fine for internet/web etc. A 500mhz 'book will do all the basic stuff no hassles.
I say go for it if you can get a good deal on one. I've seen OS X run on a 333MHz Lombard, a 366MHz iBook, and a 350MHz B&W G3 and it ran fine for basic tasks.