My grandmother has a 32 inch Sony 4:3 Trinitron from around 1996-97. She's 89 years old and leaves the TV on almost all day when she's at home, so it probably has logged quite a bit of use. The TV has died twice (both power supply related). The focus/brightness of the TV isn't what it once was, and the last time the power supply was serviced (it is under a "lifetime" service contract which they consider 10 years for a TV) I mentioned it to the tech, having seen what happens when the picture tube starts to go, and sure enough it is pretty much toast. He used one of those CRT rejuvinators on it and it helped the brightness quite a bit but as for how long it will last is anyone's guess. I have an older Sencor one of these myself and have occasionally used it on a dying smaller TV picture tubes, basically it works or it doesn't, and for how long, there isn't much way of telling. Technically the last repair shouldn't have been covered but they did it out of good favor.
From my experience most TVs last about 10 years under pretty heavy use, more often than not the picture tube lasts longer than the other components in the set. This doesn't matter if it is Trinitron or not. I've seen some cheaper no name stuff with no name tubes have the tube suffer noticable brightness loss and other anomolies earlier (one such was a Changhong 27 inch using a chinese tube which is about 6 years old).
Less regular use? I've got a few sets (like an early ProScan from around 1992, a Zenith from around 1995, a Sharp from around 1996), that don't receive quite the level of use as some of the ones I mentioned above. They're still working, and in most cases still look good. I've found larger tubes don't seem to hold out as well as smaller tubes. I have an AOC 13 inch TV from 1987 that was used at a furniture store that went out of business for display purposes but never powered on and looks as good as a 13 inch TV you'd buy today in terms of picture brightness.
The newest picture tube sets I have are a Samsung 27 inch HD set from a few years ago and a Sanyo HT30746 widescreen. Time will tell how they hold up.