there are usually fairly large drops the first month or two, but then it slows down quite a bit. More like what you'd expect on a regular diet. After the first month, I lost about 8-12 lbs a month until maybe month 7 or 8, then I dropped down to about five pounds a month, and after the first year, it really slowed down to a crawl - a couple of pounds a month. I finally stopped losing at around 20 months out.
of course, some of this depends on your starting weight, age, gender, genetics, metabolic rate, etc - but it does seem to be the general pattern, at least...