Black is a great color for design. Aside from the sharp contrast it can give to other colors (especially white), black also comes across as sleek or elegant, and is a great base color on which to design. Black has a slimming effect when worn as a color, and plays a crucial role in web design (often for text or as a background). However, too much black can be overwhelming and strain the eyes when used in design.
When used in business card printing, black can provide either an element of sleek and sheer style, or a refined and elegant feel, or if textures are used, black can also provide a grungier feel.
Check out these great examples of black (and very dark gray) business cards.