We have spent a good deal of time looking at the psychological drivers of blogging & social media. 

Group dynamics, for example, are a key motivator for our clients. We sell our tool to a team of experts to enable them all to have a stronger voice online through their blog, social channels and newsletters. 

We have seen again and again that it is important for more than half of any group to be involved in an activity for it to have a social acceptance that drives its usage.  With that, the usage will creep up until everyone uses it. Then the whole team get the benefits...

If you are short of content ideas, I recommend you read Neil's post below. A ton of good ideas (though sadly no insight into the magic effect of an odd-numbered list!)