Just to note...I am defining "bowling" as directly linking to a competitor's site.

I have never observed a "once removed" bowling effort (this is, linking to a linked site, and not directly), and I would have a hard time finding one using standard link analysis.

That seems very obscure as a tactic, to me, but I guess, like everything else, people might have tried it. That's a massive amount of work for a subversive attack.

If the goal is to create an appearance of a closed link network, there are more straightforward ways to do it.

BTW - the best defense against that (closed link network participation) is to have a lot of links (both in and out) that are not part of the network.

I have seen sites that have participated in these closed link networks successfully maintain their rankings if they substantially dilute the "closed" effect of the network links. Real estate is notorious for these "closed link networks".

The "bad neighborhood", sky-is-falling scare tactics that run rampant out here are not really that significant, if a site has a lot of legitimately obtained links. There appears to be a "threshold percentage", and it seems to be pretty high.