I think most of the boards are good. Granted, there are only 5 or 6 forums i post on regularly, but everybody has their own taste. If you're trying to save space, its one thing. But if you don't need to save any space you might as well not delete anything until the community demands it.
If you must delete...look at the forums that are redundant. There are like 5 different forums under the Art section. I'm not sure if you need all 5, because i never visit any of them, but to me it seems like overkill.