Ignore mberan, he's totally wrong.
kubuntu 7.04 is where it's at.
I actually just the other day formatted my Vista partition and expanded my Linux partition.
There are genuinely no reasons that I can think of to have Vista, other than, possibly, to boast about having Vista to people who don't know how pointless it is. It just doesn't have any advantages over XP, except a prettier interface. And if I pretty interface is what you want, I've already mentioned kubuntu, which has a much more customisable GUI (kde if you don't know, which I prefer over ubuntu's GUI, gnome) than Vista, and since you're not bothered about gaming, there is no drawback to having it.
edit: I just realised I didn't really say any reasons that you should upgrade to Vista. That's because, and I can't stress this enough, there aren't any.