I'm a professional developer for a consulting company. I don't go onsite with clients often, but it does happen (so I don't use business cards often, but I have them). My employer is in the process of replacing all business cards (new head office address), and has asked that we provide our LinkedIn URLs to appear on our cards.
Should I care/object? I tend to have a high degree of concern about privacy, and this request bothers me, but I can't really articulate why (which makes me suspect I'm overreacting). I'm not looking to change jobs, I like where I work, etc. I guess I feel that my LinkedIn presence is a personal resource and not a corporate resource. On the other hand, the only likely outcome is additional professional connections on LinkedIn, which is probably a net positive should I ever want to consider other opportunities.
Edit to clarify: I do recognize that LinkedIn is not a private resource in the way that, say, a Facebook page is (although it does allow privacy controls). What I meant to say is that I view my LinkedIn page as a personal resource for making professional connections, not as my employer's resource for marketing, and that my general concerns about online privacy make me tend to be concerned anytime I feel like a line is being blurred.