Do you think it is worthwhile to run linux on a laptop? Pros and cons?

Well, there are pros and cons...

Linux is more configurable, so it's possible to do a lot of things like increasing battery life. Making better use of hardware, etc.

Currently there may be more cons than pros though. You'll have to deal with a ton of the most difficult parts of Linux all at once. If you're experienced, this is no problem, if not, it can be quite a pain. If ACPI doesn't work right away, you have no power management for your laptop. No battery monitor, no low power mode when on battery, sometimes no fan control. Often times you won't have frequency scaling. If these things don't work, it requires recompiling the kernel. If you don't have an Nvidia or ATI graphics card, most likely you won't have 3D support for your video card. That may involve rebuilding X (the graphical windows manager) and MESA (video driver support). Getting wireless cards to work can be anywhere from a slightly confusing inconvenience to a big pain in the butt. File sharing is often easy, but dealing with firewall configuration to get file sharing to work is much harder in Linux than in Windows usually. The larger distros usually have lower battery life at default settings than Windows and take quite a bit of tweaking to get to good levels... out of ideas.

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:

http://dmoz.org/Computers/Software/O.../Floppy_Sized/

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:

http://www.goosee.com/puppy/
http://www.damnsmalllinux.org/

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:

http://www.tldp.org/HOWTO/Laptop-HOWTO.html
http://www.tldp.org/HOWTO/4mb-Laptops.html
http://www.tldp.org/HOWTO/Battery-Powered/index.html

Have fun!