I have an iPad 3. A friend of mine has an iPad 3 as well. Both have difficulty connecting to an Asus RT-N1-3U router with WPA2 Personal encryption, but do not have difficulty connecting to an old Linksys router.
The difficulty appears to be related to certain brands of router and certain kinds of encryption. I can enable WEP or WPA encryption on the Asus router and connect no difficulty, but have trouble with WPA2. Other routers, like the Linksys or my roommate's Netgear router, have no problem with WPA2 encryption.
I don't know if the difficulty is related to IPv6 or not. I would expect quite a few consumer-grade routers not to handle IPv6.
iOS 6.1.1 is currently available only for the iPhone 4S, and addresses a 3G connectivity problem unique to the 4S. It is not available for (and won't show up on) other devices.
