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CainIV - 5:22 am on Jul 19, 2006 (gmt 0)
It's ok to link some sites with others, but stay away from linking all of your sites with all. Most of all, only link for a reason (such as in an article or sales letter) and not from the footer of every adside or footer. Where have you hear this information? Are you referring to index page penalties due to other page duplicate content, or duplicate indexes on those various sites. Most pages of mine that inevitably got dropped or supplmental due to duplicate content never got their rankings back.
I agree with what Wizard said. Might make alot of sense to ensure, if needed one by one, that each site has a dedicated IP. But since duplicate content penalties supposedly last 3-6 months that likelihood is getting less likely because it has been 7+ months now.