If that's what you mean, no laptop is going to be acceptable. Laptop keyboards are crap. Laptop ergonomics are crap. Laptop expandability is crap.
If the question is, "does Ruby run on 2.13GHz dual core machines", the answer is yes.
I like to work from not-my-desk once in a while, so I have a small netbook for that. But honestly, it's so much nicer to work at a properly ergonomic workspace that I rarely do this -- only for hackathons and the like. If I am by myself, I am in front of a proper workstation.
(I also don't like the "well, just ssh from your laptop to a server" approach that others are mentioning. I can feel the latency. If I run Emacs over ssh or X to another machine, I notice the key lag. If I edit files on a remote file system, I feel the latency for operations like "git status" and even saving. Perhaps I am just very picky.)