toothpaste.corp.google.com - Google serp cleaner?

Trawling through my analytics on a couple of sites that got the dreaded "Google Webmaster Tools notice of detected unnatural links to..." message I've noticed the URL toothpaste.corp.google.com appear as a referrer a few times over the last few months. A bit like the sites might be have been reviewed.

There doesn't seem to be a lot about it online, other than that and many other similar ones (Few others on here: http://googlesystem.blogspot.com/2006/09/behind-corpgooglecom.html) appear to be part of their intranet.

Has anyone else seen this or similar appear in their analytics prior to the unnatural links message?

Be good to identify which ones mean a review has taken place to act as advance warning to anyone concerned they might be slapped!

Any ex-Google employees on here who want to share some insight as to what the sub-domains on the Google intranet have on them?!

A more complete list of the subdomains here:
http://ruscoe.net/google/google-subdomains-internal/

To give a bit more detail, I got visits every 2 weeks for the last few months, before seeing the message appear in both sites after the last visit.