It's about friends and associates.
(And faces too.)
In recent months, many people want to friend me on Facebook with a company logo as their photo.
I say no to these requests.
I'm fine with using Facebook for business purposes. We all have personal lives, family lives, and professional lives and these are appropriate ways to use Facebook.
But if you're tempted to use your logo as your Facebook image, I'd suggest that you re-think this.
Instead, create a personal profile with a photo of you. Here are ways to do your photo.
Then create a Facebook page for your business. Facebook Pages is the way that brands (with logos) should engage.
It's different with Twitter because there is no difference between Twitter feeds. I do follow feeds with logos on Twitter if I recognize the brand.
What about you? What do you do with friend requests from logos?