This really is a great operating system - and unlike Windows it is completely free (if you download it from their web site - or just a small amount to buy the CDs as here). It is faster than Windows, uses less resources, comes with a full office suite and is (in my view) better looking than Windows or OS X. (Okay, to be better looking than OS X you need to configure it a little, but that is the beauty of it - highly configurable). The Ubuntu community is very friendly and knowledgeable and read to help with any issue you might have. You can install this along side Windows or just run it from the CD and see if you like it.
If you don't play the latest games then there really isn't a reason not to try this (- unless you scare easily :-) ). Even many of the latest games will play well on it (though that should be treated as a bonus rather than necessity) - I have Doom 3 running on Ubuntu and it plays very well.
Give it a go - what have you got to lose?