And the above post by Dave - is the best so far and sums it up nicely, especially the first line I highlighted.
Facebook is a great medium for me to interact more personally and regularly with my potential, current, and past clients - a more direct and quicker method than the usual emailing etc. I still run my website and separate travel blog too.
Most famous photographers/entity run some sort of facebook page and are able to interact a lot better and faster with their fans and clients.
Who cares what the shares value of Facebook is, it does not correlate or affect photography on Facebook at all. Bad/cheap photographers do.
Its 2012, get with the times, social media is here to stay and can be utilized very effectively if you know how to, and have the time for it.