Pistol:
I don't use SL. It's good at first when you are getting used to things, but in most cases should be discarded as quickly as possible. In my experience it actually causes a deteriation in my ability to know what is going on with my chosen aircraft. I am not sawing "feel" because there is no real "feal" in this game, but there is input (your controllers) and ouput (the visual representations on the screen). So, even though I stall and get into bad flight situations at time because I don't use it, I prefer that to the alternative.
HOWEVER...
All this said, I know people that have been flying in here for years and they still use is and have great success. In their eyes it allows them one less thing to worry about in a fight. They have learned what they can and can't do so the use of SL is not an issue to them.
I think the key comes down to knowing your chosen ride making the most of it's performance, SL or no SL. I have heard people say that the stick that doesn't use SL can regularly beat the one that does. I have not found this to be true (from my obeservations). The stick that knows his ride best, the other stick's ride at least as good as them and has better SA tends to be the real determiners of who comes out of the fight still in control of his aircraft.
I'd recommend not using it, but if you are comfortable with it and are successful and are not able improve your performance without it, then use it and really learn your ride's performance with it enabled. Ultimately it is about how much you enjoy the game.