I have had some killer plateaus and this is my experience: When I stick to 800-900 calories and do the same exercise, my body gets into a rut. I have made it a point after every plateau that lasts at least 3 weeks to up my calories by at least 200 more calories for a week, and to change my exercise, sometimes making it more intense, sometimes taking a few days off, sometimes just completely changing what I do. Every single time, the plateau has broken. I don't worry about plateaus less than 3 weeks, because I think my body needs time to adjust--even when I'm not losing pounds, the inches seem to continue to come off.
This past week I was off of work, out of my normal routine, and eating what I shouldn't beating. I got on the scales expecting to have gained a few times--so time to face the music. Imagine my surprised to have lost 2 more pounds.