I like the mixture of responses. Resources, relevance and ROI seem to be constant themes throughout many discussions about social media.
I would like to add the "shiny object" challenge. So many times technology, or a platform hits the stage, takes off and everyone is talking about it, while a larger portion of a community is still trying to catch up with the technology that was the rage two years ago. If we are constantly chasing the new technology, what happens to the communities that we have built on the previous technology? Not everyone is going to want to switch and while we may gain new "friends" we really risk losing what we had.
My other concerns is how we are creating technology class struggle. If information is shared or jobs are found through social media, what about those individuals who live in communities that don't have hi-speed internet, don't have the funds for a fast computer and don't have access to the tutorials to learn how to use social media. We are losing great individual contributions to our society by only having the conversations online or through social media.