My wife had one electrician who popped a chalk line down the wall before he set the boxes so they were all exactly the same height. He said it was faster than measuring each one and gave a better result.
Greg,
I've used a couple of pieces of 4" x 1" timber (one for socket-outlets, one for light switches) before as a "story stick" when fitting my flush-boxes, mark off the height with a pencil on the stud, fit the box.
Whenever I'm doing any sort of repetitive marking out, I've always used this method and always have a few scrap bits of wood or PVC conduit with me, it saves quite a bit of mucking around measuring things individually.