I've been using the Entrecard service for half a year or so now, and I still think it's a cool way to advertise on other sites and to get advertised on by others. Especially, because some really big blogs added the service to their websites - it's not only small blogs in their portfolio, but also big ones.
And now they've started to cooperate with SezWho, a commenting service, which makes the whole thing even better. Because now you can also receive Entrecard credits by simply commenting on other blogs! And other people will comment on your blog, to get points, too! Of course, there's a rating system, so that you can mark people who comment only for points as spammers. That's really good.
And that alone is not all - for me, it's really interesting what other blogs my readers visit. The SezWho plugin gives me the opportunity to find out just that! It's easy to install with WordPress and works without any problem so far.
Can't wait to see what they come up with next!