Great when it worked.

For weeks I used JunkMatcher in its default mode with terrific results (1Ghz PowerPC, 10.4.8). Dozens of Spam emails that Mail wasn't catching, we moved into the Junk folder, and highlighted so it was easy to see how well it was working.

Then I went to the Apple Store to learn more about Spam Sieve vs. JunkMatcher. There was a person there who knew about both, and I learned how to use the train as ham/train as spam function, and how to make some of the tests "hard."

Within 48 hours of changing tests to "hard" and using train as spam about a dozen times, Mail began to act strangely: the Junk button would take a full minute to send mail to the Junk folder; the program would take two minutes to close; Junk Matcher itself would take five minutes to open - if at all. Attempts to reset JunkMatcher and Mail failed to correct the problems.Fortunately, all sysmptoms disappeared when I unistalled JunkMatcher.

Fool that I am, I'm going to try JunkMatcher again, but leave it in default mode. If it acts up again, I'll move to Spam Sieve.