I don't have internet; can't afford it. I'm also tapped into my neighbor's connection. I've been doing this for 3 years, and nothing bad has ever happened to me before. I think you're safe.
I use my neighbors crappy wi-fi (netgear) at night when my wi-fi router (belkin) gets shut-off.
But it takes some knowledge in order to track what someone is doing via there wi-fi, as since this is a open signal I don't think they would bother to do so anyways. If it was locked you would have to hack into it and then they would know if someone is using it and check who but that's a whole another story.
Don't argue with idiots because they will drag you down to their level and then beat you with experience.
Most likely they would've, yes. Since you been using it for 2 years they could have locked the signal anywhere in that period of time to prevent use from people other then who know the password. It's not locked so I assume they don't care about the fact someone else may possibly be using it.
So all in all your good specially considering you been using it this long without any complaints nor problems. ^^
Don't argue with idiots because they will drag you down to their level and then beat you with experience.