July 4th 2011 our imac was bought.
Noticed when grey screen What looks like finger smudges bottom left hand corner and a thin black horizontal line running down the left hand side of the grey screen.
On googling this i was quite amased to see what it was a design fault. I was wonderd is your IMAC newer than ours have you noticed the same issues and have you tried sending it back to apple for repair. How you got on
more about it here https://discussions.apple.com/thread/2585426?start=0&tstart=0