I think it is worth running Linux on absolutely everything that's programmable, from wristwatches to satellites.
I don't think I'd buy a laptop just to run Linux or anything else on it, though, unless I needed it for something else, anyway. I once got Linux running on a very old (circa 1995!) laptop, but I had to torture and lobotomize the laptop before it accepted who it's new boss was. Laptops also have a short effective life - it's not like you can just slap a new motherboard into them!
If you already have a laptop, then by all means, Linux would be the only thing I'd consider worth keeping it around for! Linux is always a blessing to aging hardware. I would recommend the smallest distro you can find - twofloppy installs are not out of the question, here:
You can always extend the system later, but in the meantime, you can find out quicker with a floppy distro if the machine will even take it! Next, we have small CD/USB drive distros:
I've tried both of these, and love them! If your machine has a lot of RAM, Puppy might be good because it runs entirely from RAM! It runs IceWM, though. It's humble, but does the job. Damn Small is the smaller and flashier, it keeps to 50 MB, period. It runs FluxBox window manager, so of course looks snappier. (WARNING: I am an avowed Blackbox/Fluxbox freak, so am biased!) Both distros run lightening fast...we're talking 60 seconds from power-on to desktop!
Finally, here's some HOWTO's: