With directories it's all about getting links and anchor text. Will links harm a site? Never, if they have some quality. If you like the quality of directories i think you should go for it.

Thank you all for the answers! I want to give you more details about the sites/domains. All of them have original content, but the majority are small sites, less than 10 pages and these ones to not provide such value to users. The sites are about wine, some sites offer information about all types of wine, other provide information about places to visit and buy, see, try wine, one is a portal and one or two are about wine cellars.

I know Goole knows that all domains are mine. I think reasonable and if a user comes to a site, why isn't ok to drive him on other site to find some other information? So you, as an user land on a page, and from that page i can drive you to my main site, which is an online shop that sells all types of wine.

If i let the links dofollow between sites/domains, it can be interpreted as a manipulative tactic for increasing the PR, but users will find other informations about that big subject - wine.

I know that Google disagree this tactic if your domains are not related and they are more than 2-3, maybe more, but ther information found on all sites is about the same thing, and they are so related.

I will wait more answers and points of view from you, guys!

I have multiple domains (more than 50) in the same niche. All domains are on the same ip. It is ok to link them together, or to create a piramid link between them?