This is probably it. It looks like the Wi-Fi thing is hitting at around the same time for everyone and it was working fine for me at the office, then at home until some minutes ago.Copied from macrumors and it makes sense:
Here is what is going on. Ever since iOS 4(?) there has been a feature where if you connect to a WiFi network it will try to ping this site:http://www.apple.com/library/test/success.html
If it is a success then it lets you connect, if it is not a success the phone trys to bring up what would be a Login page for corporate wifi networks. Example, public access points that have a login page, etc.
It seems that some moron at Apple deleted the file located at http://www.apple.com/library/test/success.html and that is why it is not working.
This is not an iOS 6 issue but rather a problem with Apple's website.
Still unacceptable . . .