We have put online our reports generated from our Usenet despamming software; they show information about the articles we've rejected as well as common sources of these articles. We do not issue cancels for these articles; they are dropped only locally, on our newsreader machine.
Running this software has dramatically improved the performance of our news machine, for reasons explained here.
Using information logged by our Usenet despamming software we use some of our spare time to send out form letters about newly detected excessive posts, which we consider spam. More information about this and the answers to various questions and comments is here. This activity is done on a semi-random as-is basis; we make no guarantees that if new spam originates from your site that we will either notice or send you a notice.
We do clean up the University of Toronto's news hierarchy, ut.*, by cancelling what a consensus of University of Toronto news administrators consider excessively crossposted articles. These cancels are issued with limited Newsgroups and a University of Toronto only distribution, to limit their spread. More explanations can be found on the janitor web page.
In the future, the janitor may be expanded to issue cancels for certain sorts of spam found in our organizational newsgroups.
This is only part of our stance against all sorts of network spam and abuse, and of our policy of making much of our software and configuration data available to the Internet community.