Do not bother. Something Borrowed was sold as a romantic comedy but it's really of the romantic trainwreck ilk. Despite the promise of the commercials, it has few laughs in the first half and none in the second. But let's suppose you are interested in a romantic trainwreck movie - it's a real genre and sometimes the movies can be good - there are much better ones out there.
Among the other reasons to dislike Something Borrowed include logical problems with the story, miscasting, no chemistry between the leads, and characters so sterile you won't be able to garner any emotional attachment to the movie. There's also the matter of the movie being 20 minutes too long and having two false endings.
There is one redeeming quality to Something Borrowed: the always adorable Ginnifer Goodwin. My advice? Skip Something Borrowed - whether you want to see a romantic comedy or romantic trainwreck, you can find better examples of both.