I've had two (30L) dehumidifiers for a few years now. (one upstairs, one downstairs) They are great for putting near washing you have to hang indoors, also great for a house with mould problems or for keeping condensation off windows, etc.
Two downsides are they can produce quite a bit of heat if in a small, closed room (such as a bedroom). Not a problem in the winter, but in the summer it can get rather hot. Also, DH complains about the 'humming' noise being too loud. I don't find it a problem and at night going to sleep I find it quite soothing as it's a constant 'hummm' type noise (buy maybe not everyone would like that?).
I can't recommend dehumidifiers enough. They are expensive, but I think well worth the money.