Is it not showing up at all in iTunes? And which install method did you use?
I'm asking because I had a similar problem when I clean installed SL then used the Migration Assistant to get my old apps. The iPhone would show up and sync if I reinstalled iTunes but upon restart this would stop working.
Anyway, I solved it by 'reinstalling' SL over my existing installation (you do not lose any settings/files). I'm sure a faster solution exists if someone determines what is creating the actual problem, but till then this should work.