Same problem here.
Have been updating all of our iOS devices to v6 this afternoon. iPad 2, iPhone 4 (Verizon), iPhone 4 (att), iPhone 3gs all updated and connected to home wifi no problem (Apple Airport extreme - single antenna wireless N router).
After updating the iPod touch and attempting to connect to the wifi network, connection was established and then I was redirected to a login page similar to what you would see at Starbucks (to my knowledge, the airport extreme doesn't even have a login page authentication capability...). Since unable to authenticate, it dropped the wifi. This behavior spread to all of the recently updated iOS 6 devices (dropped from wifi for authentication failure).
Now. As I am writing this, all of the devices suddenly will connect ok...
Suggest you wait a bit and then forget / re-attempt your wifi connection.. Rinse and repeat until this automagically goes away?
Note. My wifi access point is set up as a hidden ssid with WPA encryption...
I am curious if the rest of you are using airport wireless access points.. I am guessing not. This appears to be a temporary glitch with the wifi authentication Apple uses to determine whether it is connecting to a login authentication page access point. Very strange.