No one knows for sure. I think people are saying September because that is usually when Apple does their iPod event.
Fall ends on December 20th, so they have a long time to get it out! I honestly think they release around the time the next iPhone comes out. I'd say end of September or beginning of October.
It's almost like the iPhone 5 is going to be an after thought this year. We'll get ios5 and it will be like "Oh, and here's a new phone to run it on."
Wirelessly posted (iPhone: Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8J2 Safari/6533.18.5) What can you possibly gain by asking a roomful of anonymous people when they think iOS 5 will come out?
A friend of mine has an uncle who's 2nd cousin's grandmother's eldest child mentioned Sept 20th. I know this date to be accurate because said person also predicted rain the other day.