When I look back and think about what my reaction was as I sat in the theatre watching Mr. & Mrs. Smith, nothing particular comes to mind; this does not mean that the movie is eminently forgettable. It's just that I neither enjoyed any scene particularly, nor was I disgusted with any part of the movie.
The movie did have its share of good moments (car chase scene; not on account of the action, but on account of the great song that serves as the backdrop) and bad ones (the way Brad Pitt and Angelina Jolie come out unscathed from the assault in the climax -- an Evil Overlord moment in reverse, if you will).
And Angelina Jolie? Let me just say that I know I speak for the entire male heterosexual community when I say "Yummy!".