Got my Apple Cinema Display in February of 2009, and it's doing well. I've run it at full brightness during most of the last 9 years, though, which musn't have helped it.
As for my various computer CRTs, I use them seldom enough that operating them at full brightness when I do use them probably won't do much harm.
My 27" TV, however, I use at somewhere between half and two-thirds brightness, because the colors bleed like mad when it's at full (probably due to wear and tear, as I vaguely remember reading somewhere that when that happens, the CRT is probably at best half-way through its service life). We did buy it new in 2005, so it's +/- 13 years old. That probably explains it.
c