flexwatt

Not too often from what I am finding but just like any electrical item, they can go bad. I have a couple cheap ones and 2 are running strong but 1 was bad out of the box.

Thermostats don't go wrong often. But they can so can dimmers but not as frequently. The more complex something is the more components to fail. Dimmers almost always fail in cold mode, T-stats can in either off/or on. I personally run a dual t-stat set up one will shut down the other in case of failure.

However dimmers only ONLY work in a space that has STABLE temperatures and they do not change much. If you have a dedicated 'snake' room that is held at 80 (or whatever temperature) by an independent heat source (oil heater) Most people I know whom run dimmers have the heater on a T-stat (helix or herpstat in the 4 cases I can think of) The room doesn't vary much maybe 3 or 4 degrees from the hottest to coldest The rack temps vary with the room. The money you save you spend elsewhere (power, oil heater, T-stat for that) The only way you get it back is multiple racks.