I am looking into purchasing a used 5D and I've noticed a lot of questions about serial #'s. It there something to do with serial #'s on the 5D that I am not aware of?
The only "serial number" issue I know about was a firmware update issue in early 2006 (firmware 1.05) for some early 5D bodies (those with the fifth digit in serial number equal to "1") where Canon advised return of the body to one of their service centers. Below is the text of Canon's firmware update notice:
"This firmware update incorporates the following improvements: fixes the phenomenon where the images are monochrome, fixes the phenomenon where the shutter cannot be released when using the EOS 5D + EF85mm F1.2L + Speedlite580EX. This firmware update applies to cameras with firmware versions up to 1.0.4 installed."
I hadn't had a problem with this combination at the time of the notice, but sent in my 5D body to be upgraded - no charge. I don't know what the implications of not having their service center apply firmware 1.05, or whatever else might have been done to the body while in their facility. Otherwise, my 5D has always worked flawlessly, before and after 1.05.
The 1DMIII is the only Canon camera that I am aware of with specific serial number issues. Whatever 5D you get, make sure you install the latest firmware and you should be good to go.
1) 2008: 3xxxxxxx; 2007: 2xxxxxxx; 2006: 1xxxxxxx; 2005: 0xxxxxxx
2) Latest model has better AA filters (Somebody told me S/N 122xxxxx or larger number)
3) your best bet is 2007 and later
of-course you can get a new one with an older serial number - hope this help