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On Twitter however, I find myself more like to be following/ and followed by more people who might be interested in the php post.
So as I say, take everything on it's own merit. If the like button suddenly causes every site to slow down and spread viruses then by all means remove it. If it provides value to your site and your users then I'd say keep it.
Do people really use those things? I don't.
I don't remember the thread, but people were complaining the Facebook Likes on the home page were slowing it down, perhaps it's being fixed or dropped lacking any performance enhancing solution.