Two pounds of fat loss a week is ideal. As you burn fat, you also release the other things stored in the fat. If you have had a bad diet up until now, that can result in opening the floodgates of bad nutrients in fat, so keep that in mind if you lose more than two pounds a week. Also take into account that water loss can tip the scale one way or another.
Perhaps the best thing to keep in mind when on any diet is its not about weight. You may be losing fat but also gaining muscle. If thats the case, which it probably is, the scale should not be your primary tool. Have your body fat % measured using a reliable way (as detailed in Ferriss' book) and measure your body (waist, arms, legs, chest, et cetera). Body fat % and body measurements are more of a pain than just stepping on a scale, but they are more reliable.
And to reiterate Kay's comment, look at the big picture. Wait a month before taking measurements seriously.