Something Wonky This Way Comes

Apparently some nefarious malady has stricken my WordPress install – now all commenters, unless they are registered and logged in, show up as “Anonymous” when they attempt to post. I am working on a solution and am currently trawling the WP support forums for any hints.
When I find a solution, I will attempt to backtrace all “Anonymous” comments and properly attribute them to their respective authors.
*sigh*