I've actually used it as the primary system on an old dell P2 233 mhz laptop.
Great little system, it comes with everything you need in ultra-stripped down form. It's about as resource intensive as windows 98 (it'll run well on 64 MB of RAM), but you get a modern kernel and USB features.
The one thing I would do if you install it to your HDD is run the Firefex downloader and installer. Dillo (the main, included browser) is nifty in that it's only 300kb, but it sucks pretty hard on rendering modern webpages (basically no CSS support). But dang is it fast.
EDIT: Whoops, I just realized I was talking about Puppy Linux, not DSL. I like puppy better.