I have done something, too, I wouldn't call it heroic though either.
I was walking home from a friends, and on the way I had to pass close by some woods, with a playground next to it. It was kinda secluded, you could see it if you were looking, anyway nobody was around besides me. Until I got closer, I walked by the chain-link fence (surrounding the playground) going along the path to the exit of the little patch of woods. Anyway, I looked in and seen this, to be honest, dirty gentlemen in his mid-40's talking to 2 kids that had to be in grade 2 or 3 at least. First, I thought "PEDOOOOO LOL"
Then I really though about it, and wondered if he was. I watched him, and instead of walking along the path to exit, I circled around the parameter of just watching him talk to these 2 kids, I didn't want to rush in and yell or something, he could've been their dad or something, i didnt know. Anyway soon he knelt down and was like given the kids stuff, it was like the classic "dont take shit from strangers", so I go back to the entrance, and just walked into the playground. I kept looking at him, trying not to make eye contact (I had my ipod headphones in, but it was paused so i could hear). I sat on a swing like 20 or so feet away and I could hear him.
He looked over at me, I glanced away, and I heard him say
"shh boys I have to leave" or something like that
Anyway he took whatever he gave them back, and just walked out of the playground..
The kids kinda just stayed there, and started playing. I asked them on my way out if they knew that man, and they said "no we just met him" something like that. That really freaked me out. I stuck around the woods until the kids left, just to be sure the guy didnt come back. Who knows what have might happened.