My theory on Ben killing Widmore.
Before the smoke monster arrived Ben, Widmore, Richard, Miles, and that one girl were by the secret closet room. After Richard and Ben decided to confront the smoke monster Ben ask Widmore for the walkie talkie so that he could communicate with Miles.
When Ben and Flocke re-enter the closet Miles is nowhere to be seen. Ben then kills Widmore and walks out with Flocke and no mention of Miles is ever made.
Bens reason for killing Widmore is not a suprise and vengence is something that Flocke could understand. My theory is that perhaps Ben and Widmore have been working together the whole time....or maybe Ben thought of this on the fly....but it stands out to me that Miles can listen to the dead and Ben just killed Widmore and has a walkie talkie connection to Miles.
Perhaps there is some secret that Widmore can tell Miles or that Miles can read from his body that can help Ben out. Which would also help out the Losties...assuming Ben IS on their side...
Anyways it's not much of a theory but it is something I noticed...what do you guys think?