Apple has issued iOS 5.1 Beta 3 (Build 9B5141a) to developers. At first this update was only being pushed out to test devices over the air. Apple later posted the update on their iOS development portal.
There are two big(ish) additions to this build. The first being the reintroduction of of the “Enable 3G” switch in the Network section of the settings app. This switch, as it was implemented in versions of iOS before 5.0, would allow users to turn off 3G cellular data access. The ability to turn 3G data on and off will help to save battery.
Alongside the Beta 3 of iOS 5.1, Apple has also issued Xcode 4.3 Developer Preview 3, and Apple TV Software Beta 2.
I do not believe that we will see iOS 5.1 in the hands of the general public until sometime in March. The next-generation iPad is expected to be released sometime in that timeframe, and there is evidence in other builds of iOS 5.1 that points the introduction of quad-core processors in a new iPad model. On a circuitous note, I do not believe Apple would be building in quad-core processor support, unless this hardware introduction was just around the corner.