In a similar vain I quite liked Sommersby (Richard Gere, Jodie Foster) because it always has this "is he, isn't he" edge to it and you're never really sure either way. It's a slow burner and probably not to everybody's taste but it is well acted, very compelling and, for a romance, not too schmaltzy.

swinefever, that's a good one. And the 'is he isn't he' dynamic derives from the typical construction of the assumed identity type, where we KNOW the character has made the switch.

I've liked Paul Mazursky's Moon Over Parador for an assumed identity story. It precedes Dave by a few years but has a similar construction. Richard Dreyfuss' as actor Jack Noah on location in the mythical South American country of Parador must assume the identity of a dictator who has died. It is not entirely successful as a comedy because Mazursky made the curious choice of starting this movie at the end. So, (spoiler) we know Jack survives which takes the tension out of the film itself. Still, Dreyfuss works hard, Sonia Braga is delicious and Johnathan Winters is outstandingly hilarious. If you have not seen it give it a try.