Just over a year ago we bought a heated (150 watt) bird bath & stand from Wild Birds Unlimited. We used it through the entire winter of 2013-14 and it performed well. We regularly experience temps below -20 C through the winter so I make a habit of bringing it (just the dish) in each evening and redeploying it with fresh water each morning. I reasoned that this would save us on electricity, lower the risk it getting knocked over by easily spooked nocturnal deer and perhaps lessen the wear on the heating element.
It performed well enough and while some have complained about the flimsy metal stand, this wasn't an issue for us as the feet of our stand were frozen fast in snow and ice for the entire winter. Others have lamented that their bird baths didn't attract birds. Ours sure did. Pretty much all of our regular feeder visitors drank and some of those also bathed. I've read some fretful comments that tempting birds to bathe in subzero temps will lead them to icy premature deaths. That's just hokum.
Alas, the heating element in our unit failed after a few weeks of sub-zero weather this fall. I took it back to the WBU franchise in Edmonton last week and they gave me a replacement with no hassles. Thanks WBU! [I've since learned that the product's warranty lasts four years.]