When Everett puts the ring on Julie's finger, the father (Kelly) is looking from behind Everett. When we see Kelly from the front his glasses are on top of his head. When we see him from the side, his glasses are on his face.
When Ben is telling Meredith not to dilly dally, his shirt is outside of his pants. When he is talking to Everett, his shirt is tucked in.
When Meredith gives each of the Stones the framed photograph of a formerly pregnant Sybil, every one is in a somewhat plain black frame with a small white matte. Assuming that one of those frames (most likely the one gifted to Sybil and Kelly directly) was intended to be the one hanging next to the family Christmas tree in the final shot of the film, one can see that these are two totally different sized, matted, and designed fames. The one at the end is a much larger, more ornate frame with a sizeable black matte. Clearly, they could have had the picture re-framed in the ensuing year, but we can infer that each was identical during the gifting scene because of their uniform wrapping and the fact that we see more than one of them opened on screen, and all are the same.
When Meredith is having her turn at charades, the camera is placed behind Amy and at this point, Rachel McAdams has her buttcrack showing.
Some scenes of the Family Stone's New England town were actually filmed in Madison, NJ. An aerial shot of the town square clearly shows a New Jersey Transit train pulling out of the station.
Over Amy by the window while the family is gawking at Meredith outside when they first arrive.