I do realize that there is the occasional lemon out there but my experience with Canon is that that's the rule and not the exception. Let me explain...
Bought a used Canon D30 (yes, D30, their first consumer DSLR). That actually worked well.
10D - Sesnor developed an unreasonable number of dead pixels (we're talking ISO 100). Sensor replaced
20D - First one was DOA, the second one had buffer lock issues.1
1DMkII - It went to CPS for repair 4 times. For the 1st 6 months it had a SERIOUS bug, where every 2000 to 3000 shots it would stop writing to the CF card. Now if I had warning that this was happening it wouldn't have been as bad but what happened was that it continued to release the shutter after the failure had occurred and was showing the previews on the LCD making you think that it was still recording the images. So it was writing the data to the buffer (which is why you could see the preview) but it wasn't transferring data in the buffer to the CF card. Of course this always happened a critical time like the processional when the bride is walking down the aisle. Canon looked at but claimed they'd never seen that before. I know I wasn't alone because I found several other professionals who'd experienced the same thing. They'd just assumed it was user error on their part when it was not. The bug was mysteriously fixed 6 months later with no mention of it in the release notes.
5D - Was producing errors all the time. The design of the grounding and shielding design was faulty and never fixed. If you took numerous shots in a row and focused in between shots (it was even worse in continuous AF) it would cause banding. The higher you went in ISO, the worse it got but I'd had the problem show up once in a while even at lower (800 and below) ISOs. Canon claimed it only happened with older lenses that had an older servo mechanism however I experienced this issues with every lens I had. The poor shielding of this unit meant that you also couldn't mount certain Quantum batteries underneath it. I had another issues with that camera as well, can't remember what it was but it also caused me down time and forced me to rent (I always have 3 bodies with me when I shoot). Canon replaced the sensor on this camera. It was a little better but the problem was still there.
1DMkIII - Oy. Even after multiple ECOs and firmware updates, the camera could never focus on a couple walking WALKING towards me in overcast light.
70-200 2.8L IS - Image stabilizer failed and had to be replaced 4 times. By 2007 I was on my 5th IS replacement. This lens was notorious for that sparking threads that were epic in length on multiple forums. They seemed to have addressed the issue in 2007 as it was reliable after that.
24-70 2.8L - Had to return 1st copy due to some pretty egregious chromatic abberations. The replacement was decent in terms of IQ. Never had any backfocusing issues with it. It was a really good copy, my best Canon lens. Slightly after the warranty expired the zoom ring started binding (Canon to their credit did fix it for free).
100-400 f/something to something L IS- Barely EVER touched this lens (as in I think I used it twice). I had the need to use it for another gig to find out it had gone completely limp (errr... soft).
16-35 2.8L MkII - Soft on one side. I had to send it back THREE times in a row before they actually fixed it.
50mm 1.4 - The first copy I got had TERRIBLE chromatic abberations and it was extremely soft. Even at f/5.6 this lens was soft. 2nd time around I got a good copy.
85mm 1.8 - worked fine
Flash systems (550 EXes and 580EX) - SO incredibly unreliable. In ETTL they'd sometimes dump at full power, or they'd fire but would be out of sync with the shutter (and we're talking shutter speeds of 1/30th of a second here so that's a pretty big error). Sometimes it would fire off the pre-flash but never fire the flash. Canon eventually replaced a few things in 'em and they seemed to be good after that.
In the period of 1 month in 2008 I think I had to send in 5 pieces of gear. One of them (the 16-35 MkII) had to be sent in 3 times before they fixed. I think there was another piece of gear that I had to send back a second time as well. At that point I just couldn't take it anymore. I decided to switch to Nikon so I decided to go in to my local dealer to check out the Nikon stuff to see what I'd want to get. I was SO amazed at how much better it was, the optics, the body handling, the build quality of everything that I ended up walking out of the store with a D700 and a 14-24. Within a month I had a 2nd D700, D90 for backup, 70-200 2.8 VR, 24-70 2.8, 105 2.8 VR, 3 SB900's and 1 SB800. I really desperately needed that switch for my mental health. I didn't realize how stressed I was because my confidence in my gear was so low. Nikon isn't perfect by any means but the gear has been MUCH more reliable and the image quality of their lenses are just in a different category altogether. I've shot with the Nikon suff for 3 seasons now. The 14-24 had to go in once (zoom ring locked), the 70-200 went in once (it would stop focussing, you'd have to press the focus button 3 to 5 times to get the lens focused), and the D700's both had the hotshoe issue (that's the only thing I have a gripe with, that's clearly a design flaw there as so many people have this issue). So that's 3 seasons of repairs with Nikon which is less than the number of items I'd have to send in over 1 month with Canon. Also unlike Canon, Nikon actually has confidence in their products as they warranty their lenses for 5 years.
When I bought the printers, I thought I'd give Canon the benefit of the doubt. Also having been an engineer I know that different design teams are different design teams so while one design team might suck, another might be fantastic. I bought an IPF61000. After the heads were replaced the 6100 became a backup machine. I used it maybe 5 times in the course of a year. It was left on 24/7 though so it could do the maintenance cleanings to prevent clogs. Slightly out of warranty both heads failed.
In my opinion Canon has some fundamental issues with their priorities regarding quality control vs. shipping something out the door to get revenue even though it's not really "done". If you eliminate the failures that were unique to me and leave the issues that other people had as well, it paints a picture of a company that just doesn't place a high priority on quality assurance (I'm not talking about manufacturing quality control, I'm talking about QA and SQA during the alpha and beta phases of development). Everything fails eventually but with all the companies and equipment I've had over the years, none of it has been as unreliable as the Canon products I own and have owned. Would Epson be any better? I won't be able to tell until I get one. There's certainly a steady stream of head clogging issues with the Epsons but as Wayne said, leaving an Epson on 24/7 and losing a bit of $$$ to self cleanings (which is what I do anyway with my Canon printers) may end up being more cost effective over the long haul.