It seems that Apple, with iOS 6, has messed up Wifi across many device somehow. I can't use the Wifi on my iPhone 4S at all after upgrading to iOS 6.0.1 - I had issues similar to this iPhone 5 post when using iOS 6.0. I upgraded to iOS 6.1 beta 2 (for Apple developers) and that hasn't resolved the issue either. I've read that people are experiencing similar issues on their iPad 2 with iOS 6.
See my previous submission: iOS 6 Kills iPhone 4S Wifi - http://news.ycombinator.com/item?id=4811540