I recall reading that there are some mechanisms the body has for holding on to a weight, making it easier to gain than to lose. Losing tends to go in thresholds, where you can lose a bit, then your body hangs on at that level for a while. You have to keep at it ("it" being more exercize, less calory intake) and eventually you start on another step downwards.

Thank you gals for keeping me at it. I seem to have finally broken through the 180-pound glass floor. 178 this morning! Woohoo!