wow, where to begin?
First dslr, 2 months old doing not-so-high-iso for not-so-long exposures, about 10 dead pixels showing up like glitter on a teenage girl's face. I didn't care if there were 18 million good ones, for that price I deserved 0 dead ones, so sent it back under warranty repair via the retailer. Tested it in the shop, straight back because they didn't fix them all. 3 times. Finally it came back good. Few months later they started showing up again, so I gave up and started using Delta 3200 instead. No dead pixels on my scanner (although the dust can be a bitch).
Mamiya 645AF, the 'safety retract' (when you take off the film back, the shutter opens and mirror flips up to protect them) has never worked since i got it (second hand, but i'm too lazy to complain and it was cheap enough). Except when it did work, when I was shooting, it just wouldn't let me shoot and it was all interlocked and wouldn't even let me take the back off. A few precisions thuds with a fist got it back to working without losing a frame. Oh yeah, and it also sometimes decides halfway through a roll that it doesn't have a film in, so winds forward and resets to 1, losing a few frames at the end of the roll (not sure if it's just one back or the camera). Did that again tonight trying out my new 35/3.5 a few hours ago.
EOS 3, worst problem was that it re-wound after 12 frames, on a home-rolled film that I swore had 36 or so frames. I re-loaded it and it again got to 12 frames, so I presumed it was actually a roll of 12, that I'd just forgot to mark it as 12, so I just devved it. 12 good shots and 24 blank ones came out. (but still, I probably just wound the cartridge wrong). That, and it stops focussing with my 40/2.8 Pancake, but that's a known bug in the lens (and I don't have a $4k digital to upload new firmware to the lens).
Kiev 60 worked fine for the first few rolls, then one day decided not to wind a full stroke (or I loaded it wrong, a high possibility). Lost the first few frames taking shots on the backing paper, the rest were all run together (645-shape or so salvageable), and 2/3 of the film was blank.
Kiev 88CM has actually been quite reliable, despite all the warnings and horror stories I read before I bought (second-hand for <$100), but I borked up the dark-slide seal-thingy on a back a few weeks ago putting the slide in, so now it probably leaks. Got about 5 backs coming from fleabay as we speak, at least 1 I know doesn't work so it can sacrifice some parts to fix the first.
Nothing else, really. My P6, Bessas, Retinas, even my Agat 18k have never given me a problem. Neither has that Nikonos V I bought from a workmate 6 months ago, but then all I've done is load it and not shot anything, so I won't know until I do...