I have an old maple desk that I got from my grandparents when they went to a nursing home, and I've been toying with the thought of refinishing it. I'm not sure if I want to paint it though, because it's a beautiful wood and I'd hate to "trend" it up, only to have it fall out of style a few years down the road.
But one way I've customized it in the past is to use place mats or table runners on the top for a little instant decoration (I've done the same thing with my laptop desk in the living room). Another thought is to change out all the plain knobs for pretty and unique ones from places like Anthropologie. I have seven of the bird knobs (top image, below), which I received as part of a wedding gift—the eighth bird's tail broke :(
I saw some very nice ones when I was there on Friday, and I thought of all the things I could personalize without a lot of labor, and without much permanence (I'd save the desk's knobs, just in case). They have a cool "Hardware Store" section where you can try out different knobs and pulls on some sample furniture and move 'em around as you like.
Now I just gotta decide if I want to mix and match, follow a certain color palette, or just make them all the same. Hmmm....