I've got CFL's installed in ceiling fixtures and lamps inverted, sideways and straight up and I've never before heard any cautions for their use. So, I looked on both the bulbs and the box they came in. The only caution regarding inverted, although somewhat indirect, is "not for use in ... or totally enclosed recessed fixture." That note implies to me that inverted is ok for some applications.
I also have, for the past 13 years an older style fluorescent bulb, a T18w, inverted in my garage. With no problems, of course. It's the type that has a solid glass cover with what appears to be two U-shaped units inside the glass. The only cautions on it are avoid enclosed fixtures, dimming circuts and small freestanding lamps (due to its weight).
I also have one ceiling fixture, inverted, that has a max of 75 watts for each of its three sockets. It's not total enclosed, though.