I use and love Ubuntu! It's one of my favorite operating systems ever and it's very well supported - there are thousands of guides out there for learning how to use it.
Its graphical user interface is kind of like a mix of Mac and Windows 7, and I found it very easy to familiarize myself with it.
As for Windows games, you can use an incredibly handy program called Wine to run virtually every Windows program out there (including WoW). Of course, it will require some tweaking, but there are tons of guides out there - just google it.
Also, you can run Steam on it, so that's a definite plus.
It's not for everyone though. Like CyberFlash said, you should get a cheaper, lower spec laptop, to see if you like it.