You guys are thinking like old-school engineers.
Where do you think the youth are hanging out? Our future engineers & designers are using twitter and facebook. I'm not a friend of facebook, I don't have an account. I use LinkedIn as a glorified address book. But that doesn't mean a business should not have a presence in Facebook or LinkedIn in order to reach out to future customers.
Twitter. I'm no celebrity and I purposefully only follow a few people and block a lot of random people that chose to follow me. But I get more industry news from twitter - immediately as it is happening - than I do from other sources. Twitter is like a news ticker for me. And, I happen to have developed some great online connections (similar to connections/friendships I have made with the members of this online community) which have helped me advance my: tasks, projects, career, and personal life. But, I also fell into the trap of wasting a lot of time with twitter - it caused too much of a distraction during the day. I have since developed better habits and that is no longer the case.
I don't want to peer pressure anybody into it, but this "social media" thing isn't going to go away with web 3.0. Either you change and adapt or you get left behind. There is business value in these areas, but you have to be cautious to not get trapped.