Coincidentally, I was just about to send you a request to connect on LinkedIn when I saw the link to your blog post in your status update on Facebook. Twitter is down at the moment, so I can't check, but I'm guessing your status is linked to Twitter. Oh, the tangled web of gen Y social networking...
The reason it's topical, though, is that not everyone agrees that they need to have a LinkedIn or Facebook profile. I gave a short seminar this week called "Introducing Web 2.0" for business, and one attendee said to me afterwards, "Okay, I know there are a lot of people on LinkedIn, but why do I need to be on LinkedIn?"
This person is COO of one of the largest cities in the Northwest next to Seattle. He is a consummate pro when it comes to dealing with people and getting big jobs done on time.
I told him something like you said above: There's no reason not to have these profiles. But that's not really much of an argument. I would rather have some data to back up that assertion. It's my next project. Find evidence that you really do need to have a profile on LinkedIn and Facebook, or that if you do, your chances of realizing career goals, business objectives, etc., are much higher.