I don't buy the "easier to understand" arguement, because anyone who can't instantly convert from inches to feet to miles after growing up using them won't be able to figure out the metric system either. It doesn't matter if they "make sense" or not because they're both so simple.
granted, math/sci problems are easier to convert with the metric system.
And any temperture scale where you can have less than no heat makes no sense. kelvin all the way!