Audio problem: Right at the end, when Emma turns to Adam and says "What do we do now?", her mouth doesn't match what she says.
Factual error: When Aston Kutcher is getting the first text from Natalie Portman, you can see his iPhone is showing June 12 on the lock screen as the current date. The text from Emma have also a date of "06/12/10" next to it within Messages app. On iPhone, the texts received on the same day should only show time at which message arrived, and not a date.
Factual error: When Aston Kutcher is calling every girl in his address book he is using an iPhone. In one of the shots you can see the screen lighten up as he's chatting to the caller. If he was really on the call, iPhone would switch off display in proximity to ear to avoid unwanted key strokes and save battery.
Other mistake: When Adam picks up Emma and is leaning against his car, he pulls a "bouquet" of carrots from behind his back, but just prior he had nothing in his hands.
Audio problem: Before showing Adam at the bar where he gets the "where are you" message, it shows a band starting a song. However, behind Adam the band have stopped playing while the music continues.