Or in ground combat if you straft just right you can fire around a corner even if the person dodges into cover.
Not to mention.. getting stuck IN the wall during a PvP match can get a bit frustrating to say the least. I do like the ragdoll effects of knocking someone way across the room. But if they could fly into the wall or a piece sticking out of the wall, that could be fixed by putting a simple clip mesh around the maps. It would be invisible, but you couldn't walk or fly past it.
*Edit* on the space subject, I think its funny when you fly up to a planet and you just bounce off of it. Destroys the illusion when you can collide with it.