I would rather see a sparse collection of useful blog posts rather than a mass of indistinguishable drivel. I guess that reflects the sort of person I like working with.

I find some of the social media sites useful but I would always advise a clean split between your personal and professional use of sites. People may see your personal public entries but as long as they are reasonable (i.e. wouldn't bring a company into disrepute) then they are likely to be ignored.