What is the difference between thunderbolt and displayport iMacs when used as monitors? Somewhat confused by the Thunderbolt/Mini DisplayPort compatibility rules, and the apple store people were unhelpful, so I ask here (maybe I should ask here first :)  Hopefully we can come to a complete compatibility matrix.

I have a 27" iMac from December 2010 ("old imac") and another 27" iMac ("new imac") from July 2011.  The first is MDP and the second is TB.  I also have a MBP from July 2010 (which is MDP)  and a MBA from August 2011.  I would like to make a unified setup.

What devices can be used as monitors for other devices?  For example, I know that I can use an MDP cable to connect the MBP to the old imac.
The following options will work for you:


old iMac as a display for MBP, MBA and new iMac. Use a mDP cable.
new iMac as a display for MBA. Use a TB cable.