Just a couple of quick thoughts on this. Declaring an emergency, as previously stated, is a CYA maneuver. They are very easy to use and very easy to take care of. And also already mentioned, you should not use the magic E word to cry wolf.
I have only had to declare an emergency twice so far (hope that's all for a career, but unfortunatly the opportunity will probably present itself again within the next 30-40 years). The first time, I should have broadcast the emergency declaration a bit sooner. I was instructing in a Piper Apache and began to get some smoke in the cockpit. I began to asses the problem and figure out an option and then took the plane to the closest field. All the approach controller got on the tapes before the avionics wiring had burned up was "Apache XXX declari. . . squeltch". We got on the ground, evacuated the airplane, airport car picked us up, short phone call to the tower and that was it.
The second was on a 135 flight in a c-421. Had a load of PAX and on climb-out noticed the oil pressure dropping. A quick glance at the left engine revealed an incredible amount of smoke pouring out of the nacelle. I shut it down, secured the engine, declared the emergency and took a vector to an airport not too far away. It took one call to dispatch and they sorted everything out for me.
A couple of weeks ago I heard a guy flying a King Air into Dalhart, Texas call FTW center and say he needed a lower altitude to "sort some things out." A few minutes later he told the controller he was getting some smoke in the cockpit. When the controller asked if he was declaring an emergency, he said "not yet" I'm going to try and isolate the problem here and figure some things out."
The entire time I was holding myself back from jumping on the mike and giving this guy (probably with much more experience than myself) a lecture, but since he had all those things to figure out, but I just let it be. Emergency declarations are a very useful tool and should be used properly. More importantly, if you have an emergengy, LET SOMEONE KNOW!!!
so much for a couple of quick thoughts.
knelson