personally : entrecard has a great tools to get more visitors but some people tend to manipulated the traffic..just imagine a blog with 15 subscribers, alexa of more than a million are on of the most expensive blog to advertise.

to get the point is easy if you are damn hardworking to drop your card to all blogs that in their database.

prior to my checking the entrecard visitors are most likely will stay not more than 30seconds, dropped the card and leave.

it is not a healhty to gain traffic from this kind of source, same like what digg.com traffic.

the percentage for the visitors to click other ads in your blog is small.
what they seek is a place to drop their card..

just my 2.5cent