This thread is interesting to me because I've been monkeying around in Planetside 2. The readers digest description of it would be combined arms futuristic combat, tanks infantry and air. The FM is basically nonexistent, it's very arcadey, wouldn't recommend it from a simmer's perspective at all. It's somewhat similar to this in that the maps are open world, 3 country, grab what you like and go kill something with it.
Here's the kicker- It has friendly fire and vehicle collisions enabled.
It uses a system where if you FF too much, it locks your guns for x amount of time (haven't actually managed to get mine locked yet, though it's been close a couple times). Looking at this game on paper, it sounds like FF enabled would be a positively cataclysmic game mechanic. It's free to play, FPS kiddies abound, and it can have battles involving hundreds of people at a time.
The thing that has me absolutely blown away is, it seems to work pretty decently. I've been playing for a week or so, and had one instance where a dolt FFed me on purpose just because. Other than that, the FF incidents I've had were pretty organic, grenade being thrown into a room I was in, people behind me shooting at the enemy in front of me, etc etc.
If I'd known FF was enabled, I'm not entirely sure I would've checked it out because of the reasons listed above, but honestly it isn't the end of the world.
Wiley.