If you can get past the sometimes gag-inducing Hipster self-love, the occasionally contrived dialogue, and the WAY-too-cutesy(but not in the way you think) ending, (500) Days of Summer is filled with many genuinely clever, sexy, moving, heartbreaking, honest moments.
That said, I don't encourage you to spend $9+ to see this movie in the theatre. But if somebody else is paying, or you can get in cheap (or free), go for it! It's worth an hour and a half of sitting in the dark.
If you can't find a way to get around buying a ticket, pick it up when it hits DVD.
[PS: Most of the obnoxious bits get out of the way in the first act. Have a little patience.]