If you updated to iOS 6 yesterday you were almost certainly having a problem with your Wi-Fi. Don't worry the problem wasn't from you, it was from Apple. Apple have a page on their website that your iPhone actually connects to in the background to check if the router has a password. So what happened was that the page was down, perhaps they changed its name or something. And what would happen is your iDevice would connect to Wi-Fi connect to the page and not find it. You would get an error saying that the page is down. Apple fixed it now and you can connect to Wi-Fi just like before.
It's funny how such a small change that happened by a web developer in Apple caused such a big issue. Be careful! Anyway is your Wi-Fi working for you now?