Facebook - keeping in touch with all my former colleagues.
Twitter - I don't usually tweet but occasionally read others' tweets, usually funny or gaming orientated. I have been known to complain to DICE about BF3 problems and it looks like I'll do the same for BF4 if I get it.
G+ - Don't use very often, and by the looks of it nor do many others, at least in my circle of friends.
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