To me, the new look doesn't seem that much like Facebook's ui; rather, it seems to just be a Google Plussification of Gmail---a natural progression.

Unless I'm missing something, basically all of the major UI elements in the new Gmail are in exactly the same place they as in the "old" Gmail.

If you squint enough, I imagine any messaging web app with a white background and three columns would look similar to either of the inboxes.