In one of my favorite scenes in High Fidelity Rob Gordan describes the making of a good mix tape. "For me, making a tape is like writing a letter. There's a lot of erasing and rethinking and starting again. A good compilation tape, like breaking up, is hard to do. You've got to kick off with a corker, to hold the attention."
I think a similar case can be made for a movie's title sequence, all be it brief, the title sequences is your first taste of a movie. It can entices you or shock you. It sets the tone for the movie, it peaks the curiosity, and sometimes a good title sequences, a really good title sequence, can be more memorable than the movie itself.
I recently discovered the art of the title site, a website solely dedicated to the best title sequences, including interviews. Looking at each title sequence, on it's own, you truly come to realize what a labor of love each second is.
... and how often it's these first second that stick with us in our collective memories.