I have lost about 34 pounds so far, going from roughly 200 pounds to 166, but only one or two close friends have even said anything. I'm sure some others have noticed, but have just not spoken out for fear of being rude (which I'm sure I actually should be thankful for to some degree.) Actually, more of my friends have expressed their intentions of keeping my dieting habits in line and healthy. Again, one of those mixed blessings. They care, but their concern is not necessary (I trust that I will not spontaneously develop an eating disorder.)
Parents: My mother noticed as soon as I lost five or ten pounds and started gushing about how thin I looked. Mothers are the best (or the worst, depending on the mother.) I'm still most happy about her reacton.
My dad has not said anything directly. He did give me a call a few weeks ago, and it went...
Dad: I'm delivering food your mom is sending over from home.
Me: Okay, I have a fridge. I can store it.
Dad: Well, it's a lot of food. We don't want you getting fat.
Okay, that SEEMS kind of negative, but he's literally never commented on my weight before, so I think that this is his way of telling me that he's noticed. Logic being that I have the ability to get fat not that I'm not... thanks dad. xD
Friends:
My closest friend at college noticed around the five or ten pound line (like my mother did), and said something immediately. Another friend was distracted by the fact that I was wearing my hair down that day and wearing new clothes, so the comment about the weight loss came as a secondary realization. But I think that was the source of her actual amazement. She was very expressive!
Which I needed. My mom's best friend went to dinner with us and was also very impressed. Now if I could just read the minds of all the other friends I know. haha
What about you guys? What was your favorite reaction?

in fact he's said three things without my prompting:

Compliments from my mom are the backhanded kind so I just ignore her, haha. But my dad has been really supportive and has asked me to help him lose weight too. For me that's been the best compliment I could get.