I've installed and used Ubuntu. It's fine, but with Linux you need to either (1) Be a master or (2) Stick with defaults. With Ubuntu, that means just stick with default package repositories, and if something you want isn't in them, you don't get to have it. (One exception: enable the non-free repository and you'll be able to install Flash, etc.)
You'll also need to do research and make sure your particular laptop is well supported: drivers can be a problem. Wireless internet and sleeping are the two biggest problem areas, followed by sound. If your hardware is supported, then you'll not run into problems.
Mark Pilgrim puts together pretty great "essentials" lists now and again: http://diveintomark.org/archives/2008/10/28/essentials-2008 . Check out past years, too.
I disagree with him about using Gmail instead of a local client, but web apps vs. native apps is a decision you have to make yourself. You could probably get away with going all web app for most everything, if you don't mind undermining everything that's good about humanity.
REGARDLESS OF PLATFORM YOU NEED TO BACK ALL YOUR SHIT UP ONLINE CONSTANTLY OR YOU'LL BE VERY SAD ONE DAY
And my advice is that Windows is useless and evil; the worst of all possible worlds, and necessary only if there is a specific application you need to run. Sadly, there often is for me. Also if I *were* to run Windows I'd wait for Windows 7, which is sort of modern, but without the headaches of Vista.