File this one under ominous -- Google Reader can't handle Google Plus feeds.
You can see this with Andy Hertzfeld's "public circle":
Google Reader can't find the feed. I thought the https was the problem, GR can't do authenticated feeds. So I tried Safari.
Safari does treat the "circle" as a feed, but the post list it shows doesn't match what we see in the web UI.
My web searches didn't turn up anything on this, which is kind of interesting too. It's not subtle!