I have used the Real Flight 7. I was practicing on single rotor heli, but I checked out a couple of the multirotors. They seemed decent. I still think even a small "toy" quad gives a better learning experience, but the sim seemed pretty good too.
It's windows only, so that limits Real Flight for some.
sure. try freerider fpv. it's $5 only and offers 5 differnet scenarios. it's los and fpv flying of a quadcopter. really nice when coupled with your real remote or an xbox360 controller.
over at giantscalenews.com we do group flying, someone sets up a server named after the site and the guys filter through over the course of a few hours. it's fun, if you guys are flying RF 7.5 we can give it a try sometime.
Don't know if a sim can do that. If they could they would likely share the downside of real world FC's using alt hold or loiter and significantly reduce the speeds the simulated copter would fly at. Wouldn't be as much fun.