I agree completely with Kjirstin-1. I'm glad she pointed out the "errors" (for want of a better word) in sdquinn2-1's post about Bruce Greenwood's age and the Viet Nam postage issue. I thought bringing that into the film was perfect; it was a great way to explain why George didn't want to bond with another dog.
And for those of us who are around the same age as Bruce Greenwood, it was even more powerful to see how his character looked during the war and how he looks now. Something we can 'relate' to, which made the movie that much more powerful and moving. On another note, I adore Bruce Greenwood, and again, in agreement with Kjirstin-1, he could play pretty much any character. He is an incredible actor, and he was perfect for that role. Noah Fisher was also incredible. I've seen him in a few TV shows (Law & Order SVU) where he was good; but he was so believable as the 'challenged' Todd. Not just any actor could perform that well in such a role.
To say that the actor dog who played Christmas was phenomenal is an understatement. This was another aspect of the film which made it so great.
So to sum up, this was just a wonderful film in every sense of the word. And last but not least, the gentleman who wrote the book upon which the movie was based expressing the need for people to adopt homeless dogs for Christmas not only added to the poignancy of the movie, but hopefully, planted a seed in the viewers' minds about adopting a pet.