It seems like a substantial part of the userbase is experiencing the inability to connect to WIFI after iOS6 upgrade (sample thread) It hit both devices I have tried (iPhone 4s and iPad2) and it looks like it's hitting most my friends too. And it's not specific to a model, people with two iPhone 4s have had one work and one not. I am not about to try my wife's devices she would kill me if they screwed wifi like i did to both mine.
I would wait for an update before trying to upgrade.
Edit: resolved it was a broken public hotspot detection "feature" linked to a page on apple's server.