I myself forget to work in scale sometime but 99% of the time I try. Initially I set up a library with scale cubes in various colours and sizes. When I model something like a building etc I use real world dimensions, which either I know anyway (Im a Surveyor) or I google. Like ctbram I work in cm, I dont know why but every time I try to work in metres Maya crashes. But its a simple scale up 100,100,100 to get metres.

cheers bullet