Continuity mistake: After Gerry gets smacked in the face by the 'broken' suspender clasp, we see the silver clasp land under the dresser. Yet, when he's moaning and lifting his leg to get onto the bed, we can actually see the clasp still intact on the front suspender that came loose, which is dangling right behind him (just look between his legs). Of course, in the next shot, that clasp is gone. Since the silver clasp is one of the plot points, this is bizarre to say the least.
Other mistake: When Holly and Daniel are at Yankee Stadium, the seat numbers in the rows behind them are not consistent from row to row.
Continuity mistake: In Ireland, Holly and William are drinking in the kitchen. Between shots, the amount of liquid in Holly's glass changes.
Continuity mistake: When Holly and Daniel are in the small room at the back with alcohol, Daniel's hair continuously changes between shots.
Factual error: At the beginning of the movie, we find out that Holly and Gerri were married when she was 19. She then turns 30, so at least 11 years have passed since the day that they met. However, when Holly sees Gerri in the pub on the day that they meet, he sings "The Galway Girl". This song was not written by Steve Earl until 2000, and they must have met sometime around the year 1996.