Excessive cross linking between any network of sites is considered risky - its just not clear where the 'line in the sand' is between excessive (and attract a penalty) and not excessive.

This is even more riskier if the network of sites are on the same class c IP address - it still can be done, but the "line in the sand" is probably moved.

Just make sure that the linking between the sites is minimal, natural and of use to the visitor and you *might* get away with it.

You may want to do a search for Hilltop algorithm (we have had threads here) in which this is discussed -- its then up to yu to make a judgement call if Google have implemented what the Hilltop documents call affiliated site (ie same class IP address).

CBP