The Facebook debate - can we take you seriously if you've never used it?

I've recently seen a flurry of blogs about the merits (or not) of Facebook as a social networking environment. I was stirred to action when I read Elsua's blog this morning, which in turn refers to the question posed by Mitch Joel "Can you claim to be in social media without having a Facebook account".

Now, whilst I don't disagree with many of the points made by Elsua, or for that matter Euan Semple, who writes about Facebook being all froth and no substance, I would like to pose the following question:

If you're serious about Social Media, and profess to be an 'expert', where there is a major gathering of like-minded socially-active individuals, can you afford to NOT be there?

Yes, there are a lot of shortcomings with Facebook, but if you want to comment about it with any authority, you need to be a part of it, not a bystander watching on the periphery.