I agree with howlingfrog. If anyone has tried installing XP on a self build...... The number of drivers to find and install and the amount of time; you can certainly say goodbye to an evening. Vista is better but.... linux just rocks in this scenario. I've had ten minute installs with most things working out of the box! And I would personally say that the install process is fairly easy in most cases, with pretty point and click gui's ;)
The problem with linux is the lack of support for proprietary software and games. I need Painter and there is no way it will run, nor is there a linux equivalent.... as for games..... well no need to say too much there!
However if you have an old PC knocking around that is too slow for vista, need a cheap and cheerful PC for the kids, then linux really can be your choice of desktop. You may need to choose a distro wisely for older hardware. But there will almost certainly be a way to get linux running; saving you money, saving the environment and giving you the chance to pick up some new skills.
Ok I am a linux fan!! However I have made many new devotees to linux by saving them the price of an upgrade. And many are very inexperienced computer users that just want to use the internet or type a letter. So I say there are two sides to this argument; and perhaps with more environmental concerns and less money around, Linux could be the perfect choice.