I've been lucky enough not to get hurt very bad playing paintball. I think its interesting that most of the "bad" injuries reported here are not so muched directly caused by paintball, but by running around in the woods in general.
My worst injury happened quite a few years ago. I was playing in the woods near a friends house and found myself semi-pinned down behind a smallish tree. I saw a very large tree not to far away and decided to make a mad dash for it. Unfortunately, I did not notice the strand of ancient, rusty barbed wire that was about knee high off the ground a few yards in front of said tree. I hit the wire going full speed and it made contact with my shin just below my knee. A spectacular forward flip ensued. My mask and equipment all went flying. My pant leg was completely shredded, but the scrape on my leg was surprisingly not too bad, it was mostly just an abrasion with very little actual broken skin. I think I continued playing after I collected my scattered equipment.
I do also have a scar on my left arm from being shot point blank on the bare skin a year ago, but I think its cool and was proud of the blood at the time. If anything, it pumped me up for more crazy bunkering.