Why do my compact fluorescent burn out within hours of installation?

Make sure the voltage and amperage coming to the light fixtures are proper for that type of light, and make sure it is steady. Voltage or amperage that varies is a killer for florescent light bulbs. Mine were doing something similar, but they would last a couple of months (when they should last years). Found out it was the current coming to the fixture was spiking frequently, which shortens the life of the bulb. It does it to regular bulbs to, but less so you don't notice it as much. Old light bulbs are pretty tough, though inefficient. Have and electrician come out and put a meter on the fixtures to see if the current is varying (this will take quite some time, not like a quick 30 second test to check continuity, which is probably what was done before)