Beginning next month, most major airlines will charge for a second checked bag. The cost is $25 a pop each way. And, if any of your bags weighs more than 50 pounds, you could be hit another $100 each way. And some are charging a $100 for checking a third bag ($25 for the second, still). These are domestic rates. International will probably be higher.
So, next year, when we're flying to Europe for eight days, I will DEFINITELY have to master the whole 'lite packing' concept.