When Wallace takes a picture of Adam and two girls at a party he holds Adam's phone horizontally (landscape orientation). Seconds later the picture received on Emma's phone is seen in vertical layout (portrait).
On their first date Adam and Emma are driving to play golf, but we see that Adam is alone in the car, and a moment later Emma appears near him.
When Adam and Emma are in the room after Adam's hangover night he puts his pants on twice,
When Emma is carrying the two cups of coffee to the car after running into Adam, she carries them like they are empty, not accounting for the coffee inside. If there was coffee in either one, it would have spilled everywhere.
Adam flinches and turns his head well before Emma slaps him in the emergency room. Not only was the slap unexpected, but Adam had taken painkillers, so he should have been far less likely to react that quickly.
When Alvin is playing the piano for Adam's birthday song, he is clearly not hitting any of the piano keys.
When Adam is talking on the phone trying to find a girl to have sex with, you can see on his iPhone that it is not really on a call. You are able to see buttons that do not appear while talking on the phone.
When Adam is talking to Lucy in his downstairs bedroom, there is a guitar at Adam's back. You can see a reflection of the mic boom in the head of the guitar and it moves down as Adam sits down.
While the fall 2010 day and date shown earlier on Emma's phone are historically correct, she later says that the approaching Friday is Valentine's Day. Valentine's Day actually fell on Monday in 2011.