I mean it, here be massive spoilers. Don't say you weren't warned.

The trailers do a good job of selling the overall concept: the plucky heroine is informed that her husband has had a fatal accident, then wakes up the next morning to find him alive. The weekdays are occurring out of sequence. Can she alter the course of history and save her husband?

For most of the movie, she doesn't even try. Monday follows Thursday, and is itself followed by Saturday, and she doesn't even seem to realize that calendars don't generally arrange them in that fashion. Eventually she catches on, but she makes no attempt to even try to alter the path of events. On Saturday, chained to a bench in the hallway of a hospital psyche ward — guess her HMO wouldn't cover an actual bed — she overhears the psychiatrist telling the cops she'd come to see him on Tuesday — before the accident — and talked about her husband being dead. Waking up later on Tuesday morning, she dutifully shows up at the shrink's office and spills her guts about her husband being dead.

But that was actually a departure for her, as she spends the rest of the film not talking to people. To her husband, whom she's seen alternately dead and alive at least four times, she simply says "I had a dream where you died" when he asks what's wrong. She makes only a half-hearted attempt to dissuade him from going on the business trip which she knows will lead to his death. She doesn't confide in her best friend — nor even surprise her by knowing the name of her new boyfriend before she's been told. She just blindly stays the course, despite knowing in advance what the outcome will be, until the morning of the accident. And then she decides she needs to try to stop it. But of course he's already left by the time she wakes up, because she apparently doesn't believe in alarm clocks.

It was not a cool science fiction tale about causality and a struggle against preordination. It was, in fact, a chick flick. Because the grand "payoff" for her week of precognition had women throughout the theater^* weeping with happiness, for even though she didn't manage to save her husband, at least her premonition allowed her to make sure she got knocked up for a third and final time.
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* Except Karen, who was as disappointed by the ending as I was.