It has been an interesting two years, with lessons in security, networking and online business.

On security, while I have yet to lock down my Facebook account following recommended best practices, I also have yet to notice harmful privacy or security break. Sure enough, there may have been that I failed to notice. And I did notice one, if harmless.
I remain convinced the main reason is my sticking to the Granny Golden Rule: only share on the internet what you would share with your beloved granny. At the very most. Ultimately, my own control on what I share is much stronger than the hoster’s control on how I share it. Facebook here is mostly special in how explicitly it encourages all of us to share more. 
The further risk, of course, is that what of my ideas I now share – say politics or religion or philosophy – becomes (more) strongly associated with negatives in my current or future community, so I end up facing negative consequences and  regretting sharing it.
Time will tell.

On networking: today I certainly use Facebook for connecting with remote acquaintances and sharing thoughts with them. 
I do so much less than I used to do two years ago. Mostly a time constraint, and competition from incoming content; sharing less to take in more.
I also have some lingering doubts about best practices for sharing content across social networks – what to share on twitter? What on LinkedIn? What on Facebook? Major content providers such as wordpress, HBR, WSJ, The Economist seem to be spreading their bets even more evenly, so I shall enjoy the company for now.
What has kept true for the last two years is that Facebook remains a very, very effective platform for sharing my thoughts with remote contacts. Just as long as I am prepared to have little control and decreasing on who gets to see what I post, once again.
I plan to keep using it for sharing ideas with general acquaintances, including funneling to Facebook anything that I am “more timely” posting through twitter. At least, when the connection between the two does work.

On online business: while I have started some valuable business exchanges, of ideas at least, on LinkedIn, over two years’ use I have yet to have any such opportunity on Facebook.
Here I believe the one difference is economies of scope: as long as LinkedIn manages to keep reasonably close to Facebook in effectiveness and ease of sharing, business intercourse will focus on LinkedIn.
I see two reasons here: first, LinkedIn profiles have been better at providing business context around what we share there. Second, many users of both LinkedIn and Facebook, and certainly most of my contacts, prefer the former for business exchanges. Ultimately, this preference keeps making the difference self-sustaining.