There seems to always be a wee boost at the start -when I first did Lt (failed miserably at it -not this time tho! ) I was around 13st and lost a stone in the first two weeks. (well -6lbs and 7lbs but you suck in the other pound!) After that I fell off the wagon so cant really say.
The first month seems to be really successful for most -then it settles to about 3/4 lb a week.
After the first 2 weeks I think most average at 3-5lb a week loss, depending on how much there is to lose and how active the person is, there is no exact science. The LT website says 1.5st a month for men and 1st a month for women.
I was 13st3lbs when I started and lost 10.5lbs in the first week I have my second weigh in tomorrow and would be happy with 3lb but will let you know my goal is to be 11st by 13/10/08