Preview at WWDC likely in June, followed by September launch.
iOS 5.1 'Pre-GM' Seed Leaked? Camera Slider, Japanese Siri
Only two new minor findings have been discovered. One is an ever-present camera icon on the lock screen of iOS 5.1. In present versions, the camera button only appears if you double-tap the home button. In this version of iOS 5.1, the camera icon is there at all times, but instead of a button, it's a slider.
Sliding up on the camera icon seems to reveal the Camera app that allows you to take photos without fully unlocking the iPhone. Presumably, this is quicker than the existing solution which actually requires the Camera app to be launched.
The other finding is the presence of a Japanese language setting in Siri. This has been rumored to be an impending feature for Siri.
Apple has been seeding developers with versions of iOS 5.1 beta for some time, but the last release was January 9th. Apple may be waiting to release iOS 5.1 alongside the new iPad which is expected on March 7th. We're not certain about the legitimacy of BlogdoiPhone's screenshots, but carriers presumably do get early builds that may not make it into developer betas.