I'll second Larrabee on excess baggage. I brought over a second suitcase, over 50 pounds, for an extra $100 at check-in on my American Airlines flight. Two suitcases and 1 carry on all stuffed to the gills. I've got some boxes back in my parents house that I need to ship over sometime though... It's mostly books that I can't replace (they have different covers over here.
USPS is semi-relaible, but it's not a good idea to ship during the holidays and your packages WILL get stuck at customs for some unknowable amount of time, longest I've seen personally was about 9 days. I had a package that was being tracked and it didn't move for that long, it took over 2 weeks to get to me. They could also cause you to pay tax or duty on the items. My friend sent me a gift last month and I had to pay 25GBP for a single framed image that was listed as a gift. *sigh*