You will undoubtably get alot of differences in opinions on the flywheel but I am going to throw my .02 in.
Typically, a lighter flywheel(or aluminum) is not recommended for street use. You lose the inertia between shifts because of the lack of weight(mass) and your rpm's tend to drop off quickly when you depress the clutch.
I get asked this question all day long every day in my line of work and all of my customers are happy that they stayed with a billet f/w verses an aluminum.
If they are racing, obviously a lighter flywheel has it's advantages and is very useful at the track. On the street, not so much.
Good luck.
Richard
__________________
Self Proclaimed "Resident Manual
Tranny/Driveline Guru"
Go with PI heads and quit watching The Fast and the Furious.
(thanks 2 IhaveadopeGT)
Remember, it is almost impossible for anyone, myself included, to diagnose a problem over the internet without seeing the car. My advice is simply that, advice based on years of experience. I don't want you or anyone taking my word as gospel. I am trying to give some direction as to what I think may be happening.
2002 Mustang gt. about to change my clutch 
