The events page ( http://events.oreilly.com/ ) has several references to a feed for the events posted. Only one of them, the auto-discovery link in the document head, is actually correct.
There's an older one ( http://feeds.oreilly.com/oreilly/events) still being referenced by the "Events Feed" nav item under the bird image and by the feed icon at top right of the table listing. The problem is largely transparent because the URL isn't even bad, just inactive.
This has been in place since around the middle of December, guessing from when my previously-subscribed feed URL went inactive.
Thanks again for taking the time to let us know about this. We're still not sure what caused the problem, but there's now a working feed at http://feeds.oreilly.com/oreilly/events.
Let me know if you notice anything else strange.