A US passport gets you into the sometimes short(er) line when going through US pre-clearance at the airport, but sometimes that US citizens line is longer than the "foreigners" line. I avoid all lines going into the US or coming back to Canada with my NEXUS card anyway.

A US passport also gets extra scrutiny in some of the darker places on the planet. I breeze through immigration almost everywhere I go, but my colleagues who hold US passports quite often get some extra attention/questioning in the Gulf, certain parts of Africa and sometimes going into China (the mainland, not Hong Kong).

"C'mon Reg, how many times do I have to remind you? Be conservative, not retarded." - (c) Rusty Iron Ring 2011