Hi guys
Apologies for the lack of contact.
I can't remember where I got up to, however I'm currently using my 3rd iMac with no problems.
After the problems before, I stormed into the Apple store demanding some proper support.
I did indeed manage to talk to the store manager: who knew nothing about the corruption.
Along with the other problems I had, he offered me ANOTHER replacement machine, however this time he gave me another new external harddrive (free of charge), so I could transfer all my data and put it on there (so at least it's safe).
We decided the best way was to start fresh, and when I needed certain photos/files, I would open them/edit/save from the external harddrive. There are still a few corrupted files here and there - however I managed to go through ALL and reprocess (?) them, which removed most of the corruption. The corrupted ones that I COULDN'T fix, I just took a deep breath and wiped them from my mac.
So far, working on my clean man, with mountain lion, I have experienced NO corruption.
If you're still experiencing corruption, I would strongly recommend you transfer ALL your files to something external, demand a replacement iMac (to remove most possiblities), and fix them from your ex disk. Hopefully starting fresh: the problem will be eliminated.
If I get anymore corruption, I will come and let you guys know.