Which is yet another reason (beyond difficulty of constant moderation) that more and more sites are just eliminating comments altogether.

I did a prelim backlink audit for a client yesterday and was finding hundreds of spammy links pointing to a blog post that had hundreds of spammy comments. The anchor texts of the backlinks are completely irrelevant to the client’s site. The severity of the issue was obvious, but I was a bit baffled as to *why* the irrelevant spammy links were being created.
Reading your comment just now made it all click.
Spammers are posting automated comments in swarms, then “boosting” them with swarms of automatically generated links on hacked domains. There’s currently over 6000 links and I’m sure it’s growing daily. They’re facing a seriously bad situation and it’s 100% no fault of their own. Wow.

It always depends on the details of the situation and the quality of the sites involved. If all the sites are very high quality, are owned by the same company, and link to each other, that shouldn’t be a problem. But, if there are poor quality sites involved, or their common ownership isn’t clear, then it could be more problematic.

It’s impossible for us to say what Google will or won’t do in any particular circumstance, but think of it this way. What Google wants are simply legitimate links. Legitimate links exist to help the user of the site. It could be perfectly useful for a user to be linked to other resources, or to link to partners in a sidebar, say, (clearly marked as “Our Partners” or such).
Where it might begin to get shady and raise suspicions with Google, in my opinion, is if there is a constant practice of interlinking between the sites that begins to look like a link scheme, and not a service to your readers.

Thanks to both you and Mark for your responses.