I have a question that I've been pondering... My main work computer is a G4 eMac 1.25Ghz. You might be asking why I'm using a PPC for work, I'm a webmaster for a church congregation and I needed a stable platform to work on for cheap. I opted into getting the eMac 1.25Ghz for rather cheaply in good condition because it is an all in one desktop mac that I could setup and not have to move or mess around with. The PowerPC arch has been my primary processor of choice for years, thus I've been using Macs a long time (m68k before that). It is running 10.5.8 and my church I work for bought me a license for PageSpinner.
Here's the real answer after all the back info, How long should I expect the CRT in the eMac to last? - I have no intention on replacing this computer anytime soon, it works very well for me. (my rule: If it works, no need to replace it) I'm just curious as if I can expect it to last a good while even due it's current age, or if I'm sitting on a ticking time bomb and might want to invest in a mini-vga adapter.
Ah, the eMac.
It really depends. The good news is, compared to other eMacs, this is one of the younger machines. That said, it is ~10 years old at this point. I have one with a bad CRT (not sure of the true cause) and another that works but has considerable burn-in - from what I can see on the screen, it was used in some sort of web based kiosk capacity.
The dead CRT is circa 2003, the burnt CRT circa 2004.
Another important note- there are several reports of eMacs with capacitors that needed replacement earlier than would be expected. Assuming you don't run into this, your CRT's life is going to boil down to (based on my experience) care given to the machine, length of use, and luck. I'd say you're well into the luck phase at this point.
Personally, I only power on my eMac when someone asks why I have a giant tooth connected to a keyboard.
In general, the CRT itself should last for a very long time -- decades, really. The problem is the power supply/analog board that drives it; the components tend to fail early due to heat. It's been a problem with Apple's all-in-one machines since the beginning. (If you could upgrade even to a 2007 aluminum iMac, you'd end up with a much longer-lasting machine as they lack CRTs.)