A friend of mind has just picked up a 50D, it has a short warranty and about 8500 shutter actuations, any known issues with this body, recalls etc. He would like to know what to look for before the warranty runs out.
On the subject of recalls, do Canon cover older models, out of production and warranty, will they cover a recall on second hand gear or only for the original owner?
Its a pretty old camera, so anything can happen. Shutters are always a weak spot, so take some images at the fastest shutter speed, and make sure there are no issues in the photo.
You can also take a lens cap photo to make sure there are not too many stuck pixels.
I'd also check to see how clean the sensor is, its pretty normal to have to clean it with a used cameras, not a big deal.
Check the clock too.
Finally, check the USB port by tethering the camera to a computer using Canon utilities. You should be able to see images live, set all the shutter, aperture and focus settings.
I don't recall any recalls or camera specific issues, just the normal things that happen to any camera.
As for Canon repairs, they reach a point where they decide that there are not enough replacement parts, and stop servicing them. They usually sell the remaining part inventory to independent camera companies, and they will do a repair is they can get parts.
Canon was still repairing loose mirrors on the 5D classic last I heard (Under the recall warranty), but that may end soon. Its something any repair shop can fix with some glue, but Canon used some re-enforcements, not just glue.
Since the 50D's now go for about $250, its usually not worth it to have any repairs made.