For business, LinkedIn can be a good alternative. There are a few others (Fast Pitch and eCademy spring to mind -- there are others) that are specifically for business generation / getting hired and the like. They're generally much friendlier toward overt business promotion than more "social" places like Twitter, Facebook and MySpace.
The important thing to remember, IMO, is that the real purpose of most social networking sites is socialization. If you push too hard on the "develop your business" aspect, you end up a pariah -- much like the stereotypical insurance salesman who buttonholes everyone at the class reunion, trying to sell them a policy.
IMO, for best results, use these sites for networking, not so much for direct selling or overtly pushing your business.