iOS 5.1 has been available in beta version for several months, however conform according to new information that appeared today, it would be released in the following days. For now, it is not known if iOS 5.1 or 5.1.1 will be available in iTunes, but this version of iOS has already gone through the verification phases and is in the last stage of testing before the official release. The GM version is currently installed on the iDevices of Apple employees and after tomorrow's conference it may be available for download, but only developers of iOS applications would have access to it.
The Gold Master build of iOS 5.1 has been in a vigorous quality assurance phase for the past three weeks, with extensive testing being done internally by Apple as well as by various carriers/partners. It is rumored to have added Japanese language support in Siri, as well as an easier method of accessing the camera from the lock screen, and at least two other new features that have not been publicly leaked. The build number of iOS 5.1 Gold Master is 9B176 according to a very solid source, although three different partners who are testing the Gold Master claim to have slightly (by single digits) higher builds numbers on their copies, I'm assuming that's because right now it'd make sense for those people to be testing what will soon be released as 5.1.1, so I've disregarded the claims.
iOS 5.1 for current iDevices will bring support for the Japanese language for Siri, a new button to open the Camera application from the lockscreen and that's about it for now. There will definitely be new functions/applications for the iPad 3, but we won't know much about them until tomorrow evening.
