I spent last night trying to help a few people who upgraded to IOS6 with the following issues:
1. App store timing out, preventing any new apps to be downloaded (ie. Youtube)
2. Lost contacts
3. Wifi not working
4. Not working with Gmail/Yahoo main
These were all people using 4S, who after upgrading to the new OS had some major issues. If you are thinking of pulling the trigger then don't right now as I had a bugger of a time trying to fix these problems (factory reset did not fix any of them, and read many threads trying to get things working). Apple 'support' communities was even down a few times last night for "maintenance."
Oh, I don't even have an iPhone anymore lol