Speaking as an Engineer, I'd never consign to memory anything I could reasonably look up. One term wrong in an equation because I thought it was consigned to memory correctly could cause disaster.
Speaking as a pilot, I prefer Mnemonics backed up by a checklist. Then, I can use the checklists when time permits, and mnemonics when...
(1) I haven't time. (This would include emergencies, en-route checks in a light aircraft, downwind and pre-landing checks.)
(2) I'm in an open cockpit and don't want to lose the FRCs over the side.
(3) Err, those are the only good reasons I can think off.
The best solution of all is when flying with another pilot / observer, use mnemonics and get them to check you've got it all right on the checklist as you go through. Some checks (such as shutdown) it's safe to do from memory then check on the FRCs yourself.
Having said that, after 50+ hours on a particular type, one can become sufficiently familiar to disregard the FRCs, but it's not a particularly good habit. I did see a friend manage an entire sortie in a Hawker Hunter without reference to the FRCs, but he did have 750hrs on type (and a somewhat above average level of ability).
G
[This message has been edited by Genghis the Engineer (edited 22 March 2001).]