Sitting here looking at a 2 hour render out of FCP, can't work on another project because Apple does not allow multiple open instances of an app, I look at the Activity Monitor and it shows over 50% IDLE. Compressor is set with a cluster of 6 processor instances.

Is it safe to say that purchasing the Octo prior to support of multiprocessors in the OS and App was basically a donation to Apples cash account for which not benefit was received? Maybe Apple will open an endowment or charity and roll some of their cash into it. I could at least write it off as a charitable donation then...

There is a way to get Compressor to use most of the multi-processor power. It has been discussed here a few times, do a search as I do not have the answer. I do not own an 8-core yet.

However I can recommend a way to use the computer without "locking it up". Make QuickTime files of your projects (leave the "Make Self-Contained" box unchecked, this will create a very small reference video file depending on how much needs to be rendered) and open Compressor as a stand alone application, not thru FCP. Drag the files in you want to render, set and go. Now you can open FCP and work on something else although I can't vouch for the response of the computer. If you are going to do this on a regular basis you might find leaving the multi-processor setup the way it is as you'll need some horsepower to run simultaneous applications.