Ubuntu is awesome, I have it on my work PC, my main and server at home. It beats the ever living crap out of XP, in Phases' humble opinion. I was on XP (regularly, I'm an IT guy) for years and years.. and 3 months ago finally went full Ubuntu and virtualized XP on my work and main home computers for the few things I still need it for.
I tried Suse 9.2 a few years back and after a few weeks ended up going back to Windows, but Linux has come a long way since then.
However... and I don't care what anyone tells you... any Linux distro, even Ubuntu, requires a huge amount of dedication on your part. You have to be willing to spend the time it's going to take to get it all setup to your liking, get it to do the things you want, and get down into the nittiest of the gritties to fix the problems. And if you use your computer regularly, there will be problems.
Hell, even just the regular security updates from the other day broke both foo and my work computers and took us two hours, working together, to fix. Turned out it was an easy fix but we didn't know what the hell it was when we were faced with two un-login-able (to X) computers out of nowhere.
You will have to be good, good friends with
ubuntuforums.org and google. Need to be a tech savvy enough person to be comfortable with command line and always mindful of making backups of files you're modifying. And you will be modifying. Unless you are the most basic of basic users who just load it, use one account to get on, get online, get off and be done for the day, you will be modifying.
With that said. I love it and I think you should at least give it a try if you're willing.
One BIG plus is any time I've needed something, for whatever, any type of program, I haven't had to search long. The package managers and repositories are awesome. Search, select, install.
Edit: I could edit and revise this post a million times so I'm going to stop here.