I have an MU install, and all our comments are being flagged as spam (Akismet history is showing "Akismet caught this comment as spam"). I'm not sure what is happening. If I unflag them, they show up as comments, yet the "False positives" count stays at 0.
For a little background info, our spam count has been slowly been increasing since May, from 6000, to over 80,000 in October. We are getting close to the 100,000 limit, which could possibly be causing this issue.