AK mentioned during the interview in-brief that it was implemented to take the place of a simulator session, the thought being that taking the Cog Test puts everyone on the same level as far as familiarity with the "gear." I suppose the argument is that it tests (in an admittedly imperfect and very rudimental way) some of the various skills required in the cockpit (e.g., short-term memory, hand-eye coordination, multi-tasking). I definitely liked not having to plunk down 2Gs or so for practice time in a 737 sim like the UAL bubbas generally do.

I found the test to be fairly straight-forward, if a bit stressful, and didn't do any prep other than to familiarize myself with the basic idea behind the various test components through the gouge that's out there. Keys to success for me were:
1 - reading and understanding the instructions;
2 - doing multiple practices until I mastered what each test was after (if you need more than two practices you have to wave the test monitor in to reset the test -- which I did multiple times on a few of the tests);
3 - not getting stressed out when I made mistakes and heard the dreaded dee-dum.