Originally Posted by mkt
I'm a US and Spanish dual national... I exit the US as an american, enter country #2 on whichever passport benefits me, exit country #2 (or 3, or 4, or 5) on the same passport I entered with, and re-enter the US on my US passport.
You do need to be careful to use your US passport when you check in for your flight if the airline scans and transmits passenger information to US immigration authorities. I did create some confusion on a recent trip from AMS to SFO by checking in with my UK passport (which I used on entry).