I noticed it at about 10 lbs but it wasn't noticable (or at least when the comments started) until about 20 - 25. I think what made the biggest difference for me was not how many lbs but how many weeks I was consistently exercising. (that took about a month for me)

Everyone I know and care about pretty well have seen the newest version of me so I don't get the "Oh, my, you've lost weight" comments as much. I kind of miss those -- they were a nice motivator. Any body else?