Here you will find some information of Google about Cross linking sites, and how you can use the Cross linking in the right way. You have to be careful the way you use Cross linking between/to your site.

Some people ask, does location of server matter?

Google webmaster said: In our understanding of web content, Google considers both the IP address and the top-level domain (e.g. .com, .co.uk). Because they attempt to serve geographically relevant content, Google factor domains that have a regional significance. For example, ".co.uk" domains are likely very relevant for user queries originating from the UK. In the absence of a significant top-level domain, they often use the web server's IP address as an added hint in our understanding of content.

O.K, can I cross-link between my sites?

Before you begin cross-linking sites, consider the user's perspective and whether the cross links provide value. If the sites are related in business e.g., an webdesign site linking to webdesign site, then it could make sense, the links are organic and useful. Cross-linking between dozens hundreds of sites, however, probably doesn't provide value, and I would not recommend it.