Front-loading NES died eventually. It probably still can work if I spend half an hour on compressive and percussive maintenance, but I have a top-loader that never fails, so why bother?
PAL SNES RF port died. But the AV port is good as gold (and uses the same cord as N64 and GC) so no big deal.
JP Super Famicom works fine.
US SNES currently in unknown status, as I removed the power socket (proprietary plug) so that I could replace it with a normal one. That was 6 months ago
N64 occasionally resets - I think it's to do with cartridge connections, because some games (Blast Corps) do it all the time, others are fine.
GC has a bad laser - killed by PSO (the data is all lumped on the disc in different places, such that the game is having to seek from outer to inner and soforth far too much).
2nd GC fine so far - but would no doubt die too if I continued to play PSO.
GB, GBP, GBC, GBA I guess still work, haven't used them in years.
GBA SP in bad nick, probably because I let it get beat up.
DS has booted to a blank white screen once.
Saturn is quite the dodgy - if you turn on the machine it's fine, you can use it for hours. But if you have it on for more than say, 15 minutes, and then turn it off and then on again, it gets nasty interference in the video output and won't boot. I figure it's got something to do with the power supply. But I bought it 2nd hand, from Cashies no less, so I don't hold Sega responsible.
DC - on my 3rd laser unit, and second mainboard. First laser unit iwas always dodgy but I didn't realise until later on. Second one was fine but eventually died. 3rd one seems ok so far.
Had one mainboard fail on me, too (just no longer output a video picture).
Flakey controller ports on my machine too, but I haven't got around to taking the ports from either of the other machines I've cannibalised for parts yet. Never had it reset-cast on me though. Crazy.
Xbox - I'm assuming it's a Thompson drive due to the problems I had (diagnosed using Twisted infamous Dead or Alive 3 endings test). Crashes occasionally. Makes a nasty crackling noise at the power point. Never bothered getting the power replacement from MS because it wouldn't have fixed the fault with the machine.
PSX - original PAL psx had a problem 11 months into ownership (barely covered by warranty). I think the laser unit locked up. Was sent to Sony, came back repaired/replaced, has worked fine ever since.
US PSX (modded) died due to a power-spike, but I was able to coax life out of it for years.
JP PSX has no problems.
US PSOne works flawlessly.
PS2 - modded pal ps2 has broken memory card slot 1 (broken by the mod ppl). Fault is on the mainboard so cannot be easily repaired. Laser was starting to go anyway.
Unmodded PAL and US slimline PS2s work fine.
So I guess I've not had the best of luck with videogames.
)...quick Candy, got to catch us all! 
