Apparently, 6 years...

Mine just gave up on me.

The flat crt I had lasted me just under 3 years which was still under warranty. I was sent a replacement and within 1 week that one was sent back when it went out. The third one lasted 8 months when it finally snapped and blew 4 months over the warranty period......consider yourself fortunate

I ended up bying a samsung.... never to be reminded of KDS. Apparently they kept sending me refurbished crap!

My Magtron 15" I bought about 10 years ago still works .... about 4 years back it stopped displaying any resolution above 800x600 (won't wake up above that), but it still works which helps as a backup. So 6 years seems to be the limit before "something" will go wrong.
I've had my 19" Hitachi CRT for about 4 years now with no signs of any trouble at all ... and it's been moved around a fair bit too ....
That said, I've been eyeing off some of the 19" LCDs we just had come into stock at work .... prices are plumetting on LCDs right now so I might have to ask how much I can get on one for with staff discount.

My DELL Trinitron 1025HT is up since 1997! (17 inch)
Still going strong.

But, my guess is that it won't last for long,. I give it another year or so.. but hey.. maybe I'll get lucky.
I paid a whopping $499 for it back then (plus $40 for shipping).

-MS2

My dell 19" Trinitron I had since abot 98 is still rockin!