I just watched this again for the second time last night, what a fantastic little movie. It's so cleverly told, not even just for a romantic comedy, but it's just good storytelling in general. Normally I wouldn't like such an insane jumping around between styles (like in a Tony Scott film), but everything works in Summer.
I remember when I first saw it in theaters, I recommended it for my friend who just got dumped by his girlfriend of 3 years, and he kinda hates his job as an accountant, and he was acting like a depressing slump. I was just like "Nate, I think they made this movie about you...!" He went and saw it twice in theaters, it's his favorite movie now.
It's probably one of the more true to the heart romantic films, which is ironic because of how crazy it unfolds. It's also motivating towards reaching your goals outside of having a relationship as well. And I like that it's a romantic comedy told from the guy's perspective. I can only relate to Sandra Bullock to a very slight degree!