I had one I bought on ebay last year and ran Tiger on it. Worked amazingly well for its age. It got caught in a water leak from my ceiling and has been replaced by a iBook G4 from eBay.
The biggest issue is the screen res is limited to 800x600. Seems most web pages are optimized for 1024x768 these days.
They're all right for basic surfing, typing, listening...but very choppy with video (avi, youtube, etc), and somewhat laggy. They'll run faster with Panther.
That said, I would really recommend saving up for a used Macbook, as it will last you several times longer than any PPC machine.