Good thread that choster linked to.

Being UA specific, let's just say that Business (C) on the 3-class international plane is superior to First in a domestic 2-class plane in terms of seat and IFE. Food and beverage will be comparable (perhaps a tad inferior). First on the 3-class plane will be even better seatwise (unless you are on the 763), IFE will be about the same as C, and food & beverage will be about the same as domestic F.