We have one in our basement, but contrary to most everyone else, ours mostly runs only in the winter. ;-) It drains directly into the sump pit and it has a humidistat on it so that we don't have to monitor it. It works great to keep the basement at a normal moisture level. We noticed zero difference in our electric bill with it, but it's so minor compared to the other things we run (septic pump, two sump pumps, hot water heater, a server room and an entire kitchen of appliances) that it didn't register.

If you can't tell from my description, we have a VERY wet basement. We live in a valley and I'm fairly certain that we are the only house with a basement for miles because it's pretty much below the water table in the winter (when it rains daily for 9 months of the year). Between the two sump pumps and the dehumidifier, we've been able to store food, wine, linens, towels and paper things (like books) in our basement with no mold problems at all, so yes..they work.