To Drop Cards Or Not, Does Entrecard Work?

I stopped dropping cards about 6 months ago. I was pretty active for a while and I did see results in Google Analytics, but I don’t know how targeted my traffic was. It did increase the amount of unique hits I was getting, but it also increased the amount of spam comments I was getting. In the end I don’t know what value it added to my site. The very nature of Entrecard feels like something that will eventually be banned by the major search engines.