Vermeil is produced by coating sterling silver with carat gold using the process of electrolysis -- an electricity in an acid bath -- to attach the gold to sterling. This 2.5 micron (100 millionths of an inch) thick layer of gold is significantly heavier than the gold applied to base metal using an electroplating process (only 0.175 microns or 7 millionths of an inch), and is therefore much more durable.
Any of Night Fox's silver pieces can be done in vermeil. So if you are wondering whether a vermeil piece is worth the investment, be assured that you will have a lovely, high quality piece that can last for generations.
Sources: Wikipedia, Red Sky Plating, BondedInfo.com