Andrea Nguyen, over at the wonderful Viet World Kitchen, has written a wonderful article for the San Jose Mercury News' Food & Wine section on the evolution - or Americanization - of phở.
VWK, the most complete Internet source on Vietnamese cuisine here in the US, has a whole lot of other great pieces on our favorite food (and a whole clearinghouse section on Viet food in newspapers and magazines), including this wonderful booklet by Sofitel Hanoi chef Didier Corlou.
And if you're cooking Viet cuisine yourself, don't miss her Mama Says section, with great cooking advice from Andrea's experienced cook mom.