I just went to my 10 year high school reunion not too long ago, and no one there recognized me. There were a couple of people that I went to school with from K-12, and even they didn't recognize me. In HS, I was a very skinny 6' 125lb kid. Now I'm about 188lbs.
Also ran into a girl that I had a crush on, and couldn't figure out who she was for a long time. She'd put on at least 50 lbs, and didn't look at all like she did in high school.