There are a couple of other threads about this, but in general, at the airports where the TSA has moved all the security screening back to the checkpoint (easily identified because you need a boarding pass, not just a confirmation paper to get through security) they no longer check for ID's at the gate. I believe it's something like 42 airports or so, they have the listing at their site.

The logic is that everybody is screened at the top of the ramp when they go through security, so there isn't need to check them again. Connecting passengers were either checked at the gate or at the top of their ramp, so unless they left their ID on the plane, they too are who they say they are.