Weight is a useful yardstick, but once you've dropped below really worrying weights, I think plateaus and whatnot are normal, and looking at measurements (both body measurements and fitness measurements) can be very useful. I know I've been plateaued for a while now, I was 207 in May, I'm 204 now. I bobbed up to 215 at one point even, but since May people are still noticing that I have lost mass around the midsection, and I'm noticing that 220-250 mile weeks aren't killers right now. Part of the latter is that I live in Illinois now, and no mountains = no effort. But, part of it is really increasing fitness. More than anything else, increasing fitness keeps me motivated when the scale just sits there refusing to play nice.