9to5Mac, and spread from there to other blogs. 9to5Mac reported correctly that the tweet referred to face detection, but then the story switched into a discussion of face recognition in iOS5. Soon everyone was writing that iOS5 would have face recognition technology built-in. A few of these articles are here, here and here, but there are lots more. (Note, by the way, that some writers got the distinction correctly, such as this article.)
The point is that face detection and face recognition are two very different technologies. Face detection is finding faces in a picture, like when your digital camera draws a square around faces and tries to focus on them. Face recognition is seeing whose face is in the picture.
Yes, it's true that Apple acquired Polar Rose last September, and Polar Rose has some very strong face recognition technology. So it makes perfect sense to speculate that Apple will come out with face recognition in iOS. But a tweet about face detection doesn't say anything about face recognition.
It's also true that face recognition on mobile is a hot area that's likely (in my opinion) to explode by the end of 2011. Google's recent acquisition of PittPatt is only the latest of several face recognition companies that Google has acquired over the years. Face.com has strong technology in the area, and Facebook is in the process of rolling out increasingly strong versions of face recognition. Possible applications on cellphones include phone security (instead of a password), auto-tagging people in pictures before posting them to Facebook, sending pictures automatically to people whose faces are in the pictures, and much more.
So yes, face recognition is a really hot area, and yes, it's likely that Apple will bring it to iOS and Google will bring it into Android. Apple may even bring it to iOS5. But even when we're reading tweets it's important to read carefully. Face detection is exciting enough, and will undoubtedly lead to lots of great apps.