Social Media - What to do where...

Answering this question: Which social media platforms seem geared towards personal use and which ones seem to work better for business?

So, I did a search for social media sites and business media sites and ~ wow!  I had no idea there were so many!  Rather than list the lists of lists, I found wikipedia has a page that does a nice job of listing and defining...

http://en.wikipedia.org/wiki/List_of_social_networking_websites

It list the focus of the sites, but, from what I have read so far, just about any site can be used to promote a business.  But it is HOW you do it that matters.  Different sites will have different methods of introducing you and eventually your product.  But the line I think summarizes it the most is 'attraction rather than promotion'.

My experience has been the following:  Way way way back... I used BBS's where you called into a host computer.  That was my first experience with social media.  After many moves to different cities and much to do... I started on MySpace maybe ten years ago or so...  But that page disappeared in one of many makeovers they did, so I gave up.

I stayed off of FB at first.  But evettually caved and joined. To my knowledge that started as a social media site but I know it is now used heavily by business.  I heard of linkedin which I was told was a professional business networking site - never joined.  Doesn't it require a fee?  Anyway, Didn't join.
I have been on several dating sites, found my wife there :)  I would guess those are social sites but I know they seriously frown on advertising.  Twitter...  Why???  I ask myself, why?  I can barely keep up with FB!   My understanding is it is short quick messages... Never joined as I love to ramble and have not been very good at being succinct.  However, business seems to be all about being short and quick and I can see the advantage of being concise in relationships in general, as, I can often remember my owns thoughts 'how much longer is this guy gonna talk!?'

I welcome your thoughts!

Karl