The Nikon D5100 is expected to have 11 AF points (just like the D3100 and the D5000). I am still getting conflicting information about the sensor: the first report indicated a 14.2MP sensor that is currently in the D3100, but the latest info I received implies that the D5100 may use the 16.2MP sensor from the D7000.
The Nikon D5000 (12.3MP) had a higher resolution sensor than the D3000 (10.2MP). If Nikon keeps this ratio, the D5100 should get 16.2MP since the D3100 has a 14.2MP sensor. The timing of releasing another 16.2MP camera seems to be right, since the D7000 is now in stock almost everywhere and is even eligible for instant rebates in the US.
I still do not have exact announcement date for the D5100 - I was told that it is "just few weeks away". The earliest possibility for a press event could be the biggest UK photography show Focus on Imaging 2010 that will start this Sunday but I have no reliable information to confirm that (Canon will not be part of this show).