Continuity mistake: In one of the final scenes of the movie, George Lopez and his wife are depicted on swings with two red wines placed on a table. The scene transitions into another couple and later George Lopez and his wife are shown again. This time they toast and drink the wine on their swings. However, in this scene the wine they are drinking is white.
Character mistake: After Reed proposes to his girlfriend, he calls Julia and leaves an excited voicemail telling her he has huge news. When Julia listens to what is supposed to be the same voicemail, the wording and tone are completely different, leading Julia to think something was wrong, such as his girlfriend declining the proposal.
Other mistake: While flying home from overseas, Kate is wearing earrings while she is wearing the Army Combat Uniform (ACU). At the time the movie took place, female soldiers were not authorized to wear earrings while wearing combat uniforms. I could dismiss this as a character mistake if Kate was a private fresh out of basic (I once corrected a real female soldier who just finished basic that was wearing earrings), but Julia Roberts is portraying a captain in the movie and a captain would have known better.
Continuity mistake: In one of the earlier scenes just after Julia has got out of bed and is telling Harrison what Valentines Day is like for women, the bathroom door behind her is shut in one shot but in the next one it is wide open as she walks towards it.