A quick update.
I took 2011 iMac no.2 back to the Apple store, this morning. The assistant said I should get a refund and wait to get the new model iMac, next month. I asked for an exchange, which he was happy to provide, and I asked if I could have one from some newer stock as I didn't want to exchange again (he just smiled at this).
Anyway, 2011 iMac no.3 is on my desk. The first thing I noticed on opening the box was that it had been re-taped. Not a good sign. Removing the clear film from the screen I noticed scuff marks on the aluminium bezel running along the top of the machine, where the microphone is. Oh dear I thought - I had been given someone else's returned machine. I started peeling this plastic film off the screen and watched as the front glass panel came off the chasis with it
The sticky plastic pulled the glass off. The sticky bit of the plastic isn't normally in contact with the glass but with the aluminium sides. Somebody did a bad job putting this baby (back?) together.
Plugged it in or rather tried to as the plug wouldn't align easily with the socket as the casework overlapped the hole a little too much.
It is now fired up and copying my life from my Time Machine back-up.
On the plus side, the white start-up screen looked pretty good (apart from the obligatory grey shadow).
If the screen is good, I think I can live with the scuff marks.