We have one. We bought a 512mb and run a 8gig SD on it.
I think it is a pretty cool little device, but in honesty, I think it is a novelty... It would be fine for several applications, but processor rich anything (non video), forget it. The video processor is pretty nice, and capable of 1080p.
As for transfers on usenet or torrents, those could get iffy... especially on torrents if you run a lot of torrents at once.
What I think the raspberry pi is good for is (lol) gluing it onto a television with a wifi chip on it. Then it will allow you to watch movies from another computer's shared drive. (legal of course
It would also be okay for a person who just wanted to type a book, or run simple applications.
Honesty it is a novelty everything, with a pretty interesting little gpu.