I had one panda cory in my 10g and he died after about 5 days. He was never really very active and didn't forage a lot. He was very active in the store where I watched him on and off for about 30 minutes.
Since I couldn't find anything wrong with him physically, I figured he died of lonelyness.
I got three arched (skunk) cory's as replacements and they are my favorites. Most of the time they are pretty independant and just go their separate way around the tank. When they rest, they generally rest within eyesight of each other (mostly in a straight line at the back of the tank). Sometimes two will rest right next to each other while the third looks for food.
The best is about an hour after a water change, when there are hundreds of little bubbles over every surface in the tank. They go crazy! The shoal together and attack the bubbles on the sides of the tank. They sort of remind me of long distance bicycle racers where one is at the front with the other two behind him, then he drops back to third and the other two move up.
The other day I caught two resting next to each other and the third found them and rested on top of the bottom two. Looked like a mini cory pyramid. I'm ashamed to say it, but it was cute as hell.
I would say they definately do better with friends.