Since we got a decent humidifier I've been surprised how much lower the temperature can be in our house whilst still feeling comfortable. It does make sense as the lower the humidity of the air, the lower the rate of heat transfer to or from a human.
We run it in the back bedroom where the clothes horses live overnight and then in our bedroom during the day. And sometimes take it downstairs. It's particularly effective in the hall at the bottom of the stairs because so much air moves past it (it heats the air so the dried air heads upstairs and more damp air is sucked through) but our hall is quite small so it gets in the way there. Note that we have a baby and use cloth nappies and we almost never tumble dry them - though we dry them outdoors when the weather is being less silly.
When considering energy costs bear in mind that all the energy a dehumidifier uses comes out as waste heat so any time you'd have your central heating on you need it on less. Drier air has less heat capacity so it takes less energy to heat a dehumidified house.
You get used to the noise, it's quite reassuring when your house suffers from damp!