During a serious job hunt you do need to be a little careful what is posted on some social networking sites. In particular Facebook, Twitter and LinkedIn. These are the three main sites a few employers will check when they are checking you out. You don't want someone to see photos of you on a drinking binge or postings that can be taken negatively. Your rants about something actually does need to be on a blog like this one your looking at (though you will probably never see me ranting).
The particular employers that will check what is posted are government employers more than most. There are a few others also that will check also but they far and few. Most won't let anyone know that they checked, here in the US that would invite a lawsuit. Governments on the other hand can't usually be sued so it is usually they that will look at your profiles.
In general, the higher the wages the greater the possibility of a social network check occurring. So, I wouldn't worry too much about it for most employers. It won't be a part of the process like the employer that I am working for at present. However, I did work at Comcast and on the US postal service help desk which did check what was posted. My recommendation is that you delete anything the most stringent employer would have an issue with. That's what I did and it paid off, I had a couple of really good paying jobs for a while.
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