I've been trying to decide the same thing with my tank... I've had it bare for the last 9 months and kinda like the extra depth and brightness it seems to give it. But I hate looking at the overflow/return lines and power chords. I thought of getting some black or blue acrylic pieces to slide between back of the tank and the overflow/return pipes to hide everything, but it still might give it more "depth" because it wouldn't be right up against the glass. Hard to explain w/o seeing my setup I guess, but it's an idea I've been tossing around. It would be easy to clean then too... just slide the acrylic pieces out and wipe everything down.
Oh, and if you go for blue, I think either a really really light blue (almost white) or a really dark blue. Don't go for that ugly bright blue you see so often... IMHO
