According to the manufacturers of these units, they cost 7 cents an hour to run. That's with the flame and heater going. Not sure how true that is but it sounds good...
We run our fireplace in the Montana alot and haven't had a problem with it yet. Like anything else, it will eventually need something replaced. I figure though, it was meant to enjoy and I sure am gonna enjoy it every chance I get and not just run it on special occasions or for when we have company.
I say run it with moderation and enjoy!
We loved our electric fireplace in the "Hannah Montana" so much, that we (okay, it was me) went out and bought a beautiful freestanding electric fireplace for home. All you do is plug it in. One of the best things is that if you don't like where you put it in the house, you just move it.