Honestly, and I think I'll get flamed for this, Forza and GT are pretty decent simulators and give you an idea about what it feels like to be on a race track. Sure, you aren't going to actually "feel" anything unless you have a wheel, but you do get pretty good physics and if you are in your off season (I hate winter), then you can keep yourself sharp by doing some laps in a car similar to your own.
Dexter, I somewhat disagree with you on point 3. You certainly can't look much farther than the apex without trying to jockey the right joystick in some fashion, but the view that you do have (even in the cockpit view) is about the total of your peripheral vision and your normal vision combined when looking straight ahead. What this means is that you, sitting on your couch, are the one to move your head and there it is--the apex to turn 1 at Road Atlanta.
It's only a game, but I found that there were some striking similarities between the way that my my F class 1994 Miata behaved in Forza and my own 1994 Miata (with roughly the same upgrades) behaved on the real track.
Your question was about skill transfer, specifically. I certainly do not believe that track time in Forza 3 counts AT ALL towards track time in a car in the real world unless you are already practiced in the real world and you are just trying to keep your apex-carving skills sharp. Try going to your very first track day, tell the instructors during the student classroom session that you are highly skilled in Forza 3, and see what they say to you (they'll laugh at you).
Flip it around, though, and I do believe that real-world track time has made me a better Forza 3 player and I think this will go for anybody.