I would like to clear about this. If an seo firm uses each of their clients sites to interlink with other, creating a seo network, what is the communitys thoughts on this, and Google's atttitude to this? Especially when the linking from one site to another is irrelevant like chalk and cheese.

Generally Googling this subject I find plenty of commentary frowning on such practices as gray seo practice, to being potentially harmful and unsustainable as far as seo goes.