Continuity mistake: When Grace is standing in the wedding dress and Karen is talking to her and complimenting her, there is a long cream-coloured ribbon which is coiled back over her shoulder. Then in the next shot the ribbon is suddenly hanging all the way down her front. In the next shot it is back behind her shoulder.
Revealing mistake: At the very start when Will enters the coffee shop, he walks over and asks the server for a coffee. The server picks up a mug, pretends to push the coffee machine button, holds the mug under the machine for about two seconds and hands it to Will. To top it off you clearly see nothing go into the mug.