The thrill of the hunt - Working for hours trying to find a skip and then landing it. Working along side another runner for Lego Lord of the Rings we found a chain of skips that basically cut out all of the section of the level (Lego Lord of the Rings - Osgiliath skip)
I enjoy watching people PB while they stream. Every PB is a special moment, and it's awesome when things can be said such as "WR pace!" without being ironic.
Another fun thing that happened the other day was the Clockwork Cat WR going back and forth. The runners kept lowering it by second after second, and they kept thinking that it couldn't possibly go faster. They might actually still be at it.
I'm with Kobe, I enjoy seeing others PB because I never feel accomplished about mine. I remember Carnage64 PB'ing Final Fantasy 7 after sticking around for the entire 7-hour plus run, that was a good time.
Every PB I get in Infamous 1. It's a long run (PB is 3:26:30) and a tough run, with lots of cool tech in it. There's just something about digging THAT deep and coming away with something special that is really like nothing else in the world (cause you bet your ass I've had 2- and even 3-hour attempts that didn't make it all the way).