This is probably not going to comfort anyone, but here goes...
Belle's 1st Christmas (2002) was fine. She was 4 months old, and didn't notice the tree, presents, or decorations. But, we were home with her most, if not all, of the time.
Belle's 2nd Christmas (2003)...Lord have mercy. We had just moved in with my mother-in-law that August. By all accounts, she transitioned magnificently. My MIL has a poodle, and they bonded immediately. She was getting settled when we would leave for short periods (prior to the move she had many "alone time" destruction rampages). When we put the tree up, she didn't really pay any attention to it...we thought we'd be OK, based on the year before, until the night of my kids' Christmas Program at school. We came home to opened presents, destroyed presents, destroyed Hallmark Collector's ornaments, and a cowering boxer on the couch that KNEW she was in BIG trouble. She seemed to know which presents belonged to her favorite child, as some had corners chewed off, but all were intact. She seemed particularly interested in any toys with that sweet, plastic smell - Bratz Dolls, My Little Ponies, etc., all had to be re-purchased, and re-wrapped. We figure this happened because we put the tree in the front window - Belle's window for surveying the neighborhood comings and goings. She found stuff to destroy if left alone in the house (with holiday comings/goings, we were left with little choice), but once the tree was down, she stopped. We've since left her alone in the house with the poodle for more than 6 hours, and NOTHING is touched. She can look out her window, and she's happy.
This year, the tree is going in the corner, and nothing goes under it until I'm home from midnight mass.