I've put them in every position possible without problems. I even have 3 in the refridgerator. 2 in the fridge and 1 in the freezer. The freezer one is dimmer but its bright enough to see everything in there perfectly well. Turns out low temps cause them to dim but I've had them in there for years and they haven't burned out or anything. I can't remember how many years they've been in there though, I put them in and forgot about them.
I have one in a ceiling fan which shakes a bit also with no problems, guess I must just be lucky with them or something.
The only light that burned out prematurely I've ever owned was the ceiling fixture in my room because it was used so often, always flicking it on and off, it's a circular electronic ballast fluorescent. It lasted for a few years also but not the rated amount which I think was 15 yers or some such, I think it only lasted about 3 or 4 years.
Perhaps a surge or something similar would be more detrimental to it or wide temperature swings that may cause the seals in the bulb to wear faster? Just guessing not sure what causes premature failure.
I have other circular fluorescents with no problems that lasted much longer than the one in this room so maybe its just a defective one or it was on during a power surge that the other weren't subjected to or just cause it's in use more. Anyway after replacing the bulb it's been working for a couple of years now so if it goes again at year 3 or 4 I'll probably replace the whole unit instead of just the bulb next time in case the ballast is the cause. I'll probably stick a surge suppressor inline on it too to hopefully deter future premature burnouts.