This thread caught my eye this morning — it started innocently enough, with a newcomer asking if it’s worth installing Ubuntu on an unused 1Ghz machine. A flood of stories follows, about using Ubuntu on a daily basis with even slower hardware.
If you need some inspiration or you just don’t want to take my word for it, you can check out the unbiased testimonials of other Ubuntu fans using outdated hardware. And of course, you could always throw in your own war stories. (I’ll try to stay out of it, since people are probably tired of me crowing about Ubuntu. )