So I've added a couple more scenarios to my testing from my previous blog post on this topic and wanted to take a second to post the results.

 

  •  iMac running and booted into Snow Leopard, MacBook Pro connected via display port and powered off.  Turning the MacBook Pro on seemed promising, as the boot screen breifly flashed the iMac into display mode.  Once the MacBook pro began booting, however, the iMac switched back to internal video and the MacBook pro was unaware of it's presence.
  • iMac shut down, MacBook Pro connected, running, and booted into Leopard.  Turning the iMac on at first seemed to be uneventful.  Once Snow Leopard began running, however, the iMac quickly switched to display mode and the MacBook pro recognized it.  DING DING DING - we have a winner.
 
The moral of the story:  If you are going to leave your iMac connected to be used as a display to another machine - make sure you boot the primary machine completely into it's operating system first.  Once boot is complete, flip on the iMac - it will boot into Snow Leopard, but then will instantly switch into display mode.
 
Another item - as I've discussed in my previous post - and contrary to what the geeks at the Apple store told me - the iMac does *NOT* go to sleep when it's operating as a display.  A couple of you have asked me if it is possible to remote desktop into the iMac while it's operating as a display.  The short answer is .... YES.  I have verified that you can remote into it and use it as a display simultaneously.
 
Another question that came down the pipe was whether there was a way, in software, to switch to display mode.  As far as I know, this is not (yet) possible.  The only way I have found other than what I mentioned above is to unplug/replug the cable to get it to switch. 
 
UPDATE! Apparently there is an undocumented feature that allows you to hot-switch the iMac between internal and external display mode by pressing COMMAND-F2 on the iMac's keyboard.  Thanks, Apple - could have saved me tons of wasted time by simply including that in the frickin' user manual!
 
Happy 27" iMac-ing Cool