It's a complete scatter for me. Here's a rundown of my primary systems and their demise (or lack thereof)
My first "computer" was a Bally Astrocade from my uncle. (it had a basic cartridge, too.) It still works great, and I just played some Wizard of Wor (Incredible Wizard, it's called on there, but anyhow...) a few months ago.
My first C64 lasted two or three years before the power supply fried itself and damaged the board to a point it was cheaper to buy a new one.
My C64C then lasted a couple years before it developed some odd random reset quirks, but by then it was old enough I sold it and my whole lot of C64 stuff to buy an Amiga 500.
My Amiga 500 was perfect. Never a glitch over the 3-4 years I had it. Sold it to buy an A1200.
My first A1200 was perfect for about a year before it developed the "A1200 AGA graphics fringe" bug (overheating Alice, but no one knew that at the time). I got it replaced under warranty just before C= went under. Second A1200 developed same issue a year later. Picked up a used A4000.
My A4000 was my primary system for about 4-5 years, until I retired it. It has stayed put for retro purposes. About two years ago, the CyberStorm MKII I put in it back when I was using it as my primary, finally gave up. It's not really dead, as eventually I'll send it to AmigaCenter for repairs. Currently, it occupies a shelf, though.
I built an Athlon T-bird 1ghz which overtook the A4000 as my primary machine. It ran until about 4 years ago when the motherboard fried. I sold the CPU to an Amiga.org member. Gave the RAM to a friend and folded the rest into my current workstation.
I built a P4c 3ghz that has been in use for about 4 years now. Still going strong.