yeah, I've got a ton of them on my legs and arms. I'm pretty sure that they only stay ingrown for a little while, because they're usually not very deep and it really just requires a scratch of the fingernail for them to come loose. However, occasionally I get some that run very deep.... and one time I had a massive one on my knee that swelled up and got infected.
On the topic of ingrown toenails, my toenails are curved a lot more than usual, so that at the sides they're almost like 90 degrees to the top part of my toenail.... so the sides tend to dig into the flesh of my toes.... I've got to be very careful when I cut the corners, esp. on my big toe. When I was 17, I had surgery to remove part of my right big toenail because it had become ingrown and got infected :Q

It looks perfectly normal now, but you could tell if you looked at the left one for comparison.