Check this entrecard review and faq to know more about entrecard. I have tried to make it as easy as possible to understand. You can ask more about that and am happy to help.
Entrecard is good for traffic IMO. I am using it at one of my blog. If someone buy adspace on your blog then you get credit for that and using those credit you can also buy space at other blogs. You have also option to buy credits. DON.
It is fun and does drive traffic to your site. It is better than most social type sites that I have tried. The downside is that it is very time comsuming to drive traffic. The best way is to drop your business cards on other blogs and earn credits. I have it on three blogs and spend at least an hour a day dropping my cards. Here is a Review of Entrecard that I wrote one of my blogs.
Many people wrote about Entrecard. I think Entrecard was better before when there was less scams than these days...
I am not sure what scams there are but you may be referring to spammers. That will happen whenever something grows and increases in users. I for one do not allow the small majority to ruin something for me.
I have two blogs on Entrecard and they do bring in some traffic. Hopefully when Entrecard get rid of the power droppers it will improve.
As a traffic service, I don't know. However, as a tool to buy advertising space, definitely a good site. Someone already mentioned this above, but it is really really time consuming. So, usually people have a drop list that they go through each day dropping...
I don't like entrecard because it's so time consuming, with allout being a perfect example of what I mean :/