Summer is a vivacious young woman (Zooey Deschanel), and 500 days is the length of time her colleague at a greeting card company (Joseph Gordon-Levitt) carries the torch for her in this visually witty, flawlessly played romantic comedy. The punning title also takes the form of an onscreen ticker that spins back and forth, allowing screenwriters Scott Neustadter and Michael H. Weber to maintain a demandingly achronological narrative and contrast the highs and lows of the hero's infatuation for wild comic effect. The gag fantasy sequences conveying his heightened emotional state are nothing new, but they're executed with such high spirits and impeccable timing that they feel fresh; a spontaneous production number, where strangers on the street fall into line with the dancing hero after his first night of romance, borders on the transcendent. Marc Webb directed. PG-13, 95 min.