In some cases, your work is your social network. I work as a sysadmin for an insurance agency, and probably the most important day-to-day function for the insurance agents here is keeping in touch with clients. The ones that are "hip" enough to know about Facebook et al can see the value these things could have in doing business, but nobody has any delusions of being able to use one in any useful fashion because of regulatory compliance.
First, the only social networking site you're allowed to have a profile on is LinkedIn, which is fitting because it's designed from the ground up to do nothing but exchange business information in the most factual and boring way possible. Access to Facebook, MySpace, and Twitter is blocked in the office by our corporate-run firewall, and if you get caught discussing business with clients on a personal profile with one of these sites, you're subject to being written up.
Second, every change, even correcting a typo, requires submitting paperwork and waiting a matter of weeks to hear a "yea" or "nay" from corporate; given that timeliness is a key factor in most social networking sites, this fact alone renders them completely useless.
Most end up passing on making a profile at all, since it ends up being a huge hassle for little benefit compared to just calling people and meeting in person the old-fashioned way. I find it hard to believe there isn't some better middle-ground that corporate entities can find which would leverage communication technologies with adequate record-keeping.