I went in my history and reclassified a few e-mails that had previously been classified as spam but should now be in the worm bucket. (Gross!) I only had to reclassify 5 - FIVE! - before POPFile recognized all the rest. I keep going back into my history to check random ones, but they all say "would now classify as worm".
Oh yeah, that's one of many useful new features added in the latest release. On message-view pages, if the message would now classify as some other bucket than the one to which it was originally classified, it says so. That helps avoid unnecessarily reclassifying stuff.