Heck yeah, you get treated differently
Also, it depends on the person and how much they've lost. For example, I've noticed a few members around here have said they have to lose a full 15 lbs. Of course other people won't notice much of a different, if any - perhaps they may assume that person is just wearing smaller clothes. On the other hand, someone like me who has to lose almost 1/2 of my entire body weight will be treated different once that goal has been fulfilled.
When I low-carbed back in 2001 (I'm making myself sound old), I lost 75 lbs - going from 235-155. I was curious as to how my classmates would react to my physical appearance because I lost this weight all over the summer, so I was excited about being thin my senior year. Well, the first day was great. A snobby blonde friend of mine, who eventually warmed up to me in that you-can-look-but-can't-touch kind of way, was so thrilled to see me and she was like "you look great," she later took me out to lunch... at her house. Girls flirted with me now and then. I had a hot date for homecoming but when stag with my friends to prom where I danced with three hotties. Even my German teacher was amazed at it. Not to mention general inquires of my life, goals, interests and just chit chat were at it's highest, but I was shy and reserved (still am), so in some ways, they might has well have been talking to my old (larger) self. Losing weight didn't give me the confidence socially, but helped me get my health back in control.
Now, as I'm in the middle of another Battle of the Bulge, I've lost 40 lbs and have realized that I am being talked to much, much more than when I was 40 lbs heavier just 2 1/2 months ago. When I was my heaviest last Christmas/Fall Semester, I wasn't very social, so I cannot gauge how people treated me. But I do realize that it is a vicious cycle: I gain weight => People don't talk to me => I become less social => I eat more => I gain weight => etc...
My marriage seems to be tanking, and in case I choose to play the dating game again, I'll be much more prepared. Now that I'm more outgoing and going to Germany this coming fall, I know that losing weight will let lose my more social side, enabling me to make more friends.