It's amazing how useful hashtags are on Twitter , if you can find communities of interest. The numbers generally lie, though. It's about finding people who actually follow hashtags. They are still pretty useless on Facebook and LinkedIn, though.
It is interesting that the most tested element in email marketing is the "subject", since that is the headline. On a poster or in a magazine, that makes sense; you can't test frequency or time of day/ So marketers are used to testing the headline. But I wonder if when it come to emails, could frequency or time-of the day (or week) make more of a difference. I am certainly not dissing the headline, but has anybody studied the relative importance of these factors?