Several websites, related topics - Cross link or not?

[ervin81]

I own several [similar] websites. Each one focuses on a particular [area]. I want to cross link the sites but want to avoid any penalty that this may have cause.

How should I do it, with nofollow or use javascript document.write?

[edited by: tedster at 7:00 am (utc) on July 31, 2009]
[edit reason] make the specifics more general [/edit]

[tedster]

There's a related discussion that's active right now about Class C and Whois information [webmasterworld.com] where Shaddows offers some great advice:

Don't hide networks. Just don't. Similarly, don't try to give your sites an artificial boost by interlinking. How you balance these two is up to you, but I'd err on the side of "if its good for my user, its good for me".

If you are linking to help your visitors but you're still worried, then just use nofollow. I don't worry, I just do what Shaddows recommends.

A word about javascript -- Google is now following javascript links in a lot of cases. They even create a "virtual link" from the script for their web graph.