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I thought the same thing last year and cross linked 5 sites. A year later they have not returned.
If you have enough incoming links to both, then you can chance it. I like to promote all sites independently now.
I don't think you will get penalized. Do it for your users and the sake of advertising, not for Google. If the sites you want to link with are your own, make sure they all have different content and different ip ranges.