Often the poster designers seem not to know what to do with all the credits they have to place in the poster, and they end up just cramming all that text in a corner where it doesn’t get on the way too much. So I think that what they have done here, incorporating the credits (and title) fully into the poster’s image is quite clever. And it ties well into the film’s title.
That said, the poster doesn’t offer much besides that bit of cleverness and Katherine Heigl looking pretty. One can probably tell from the poster that this is some sort of romantic comedy, but nothing more specific about the film’s plot.
My guess is that they are counting on Heigl being enough of a star right now to sell the film pretty much all by herself. And although her star seems to be rising fast, I’m not sure that is such a great idea.