I heard that a lot of WD were banned by Google, is it true? Does anybody know which WD were really opted out by Goggle and what can cause it?
Many are. Some that Google thought were buying and selling links/PR. Others for being spam fests. Same as other sites really.
You'll often find a grey bar for PR on directories that google doesn't like. In addition, those directories have virtually no traffic which can be seen by their Alexa traffic rating. As Mikey stated google doesn't like link sellers or spammy sites regardless if it's a web directory or any other type of site. If you're going to add your site to a web directory do a little research and make sure it's indexed by google and has some PR and traffic (unless it's brand new of course).
If you google the directory, And can not find at the first result page, It would be probably penalty by google.
We have all seen hand edits for directories and I have seen many directories that have been completely deindexed. They were spammy so no-one is hurt
In this case it was easy to see because they had 100+ directories on same host with identical categories. Latest link page had sites with keyword spam titles and descriptions and many porn links as well. It's not very difficult to identify a lot of spammy directories, but saying that a directory is 'good' is not that simple !