There are some in management who get hysterical about social networks through sheer ignorance or inability to accept change. Equally there are those in the services who are completely unaware of the damage they can cause through indiscretion with regard opsec & persec.
Can't say I've used Twitter, but it amazes me how many serving and recently left service personnel are allowing Facebook to publish their whereabouts on their facebook pages. it appears to be using their mobile phone to tell you where they are and what times they seem to be travelling. Not something I would want on a fairly open forum. But I suppose each to their own. You do sometimes see stuff that is giving away other people information which is worrying. But on the whole I think most service personnel are aware of these on-line services and what they should be saying/not saying. The RN/RM careers and the Navy in general seem to now be making a better use of Facebook for raising the RN's profile, which can only be good news.