Title Sequences

I've just read through the webpage that is mentioned in my previous post and it presents some interesting ideas. I found it particularly interesting that on their website the most commonly searched opening sequences are those that belong to the "darker" films, such as se7en, etc. I think it's true that most opening credits for those darker films -psychological thrillers, etc. - usually have more of an effect on the audience than the opening credits of a comedy/light-hearted film.
For example, the opening credits for Juno have been produced using incredible effects but as it goes on for a long time, it loses it's effect and the audience are not concerned with what's going on in the credits because they know they won't have to concentrate hard throughout the film to be able to understand what's happening. Whereas in a film like Se7en, the audience needs to focus for the duration of the film, including in the opening sequence, in order to keep up with the storyline.