MsgFiler 2.0.4 was released a few days ago. It’s compatible with Mac OS X 10.6 Snow Leopard. There were a lot of behind-the-scenes changes to how Mail plugins work, and with the help of a number of people (thanks Steve, Scott, Dane, Joar, and more), I was able to get MsgFiler updated right under the Snow Leopard release date today.
If you’re looking for a fast way to file your messages, look no further than MsgFiler. If you require more significant control over processing your messages, take a look at Scott Morrison’s Mail Act-On.
tow.com 
Thanks for the update! … it’s one of the most helpful utilities I’ve ever bought. – Jared
Hi Adam — looks like 10.6.1 broke MsgFiler 2.0.4 — when starting Mail.app it disables the bundle on my Mac,.
Sadly, just found the same here. 10.6.1 moves MsgFiler into the disabled bundles folder
I’m working on a fix. Will be out later tonight.
MsgFiler 2.0.5 has been released with support for Mac OS X 10.6.1.
Thank you for so quickly updating your utility. Of all the add-ons I use and which break after an OS update, MsgFiler is the only one whose breakage makes me stop and plot steps to roll back. I can’t use Mail.app without MsgFiler and your dedication to the tool is an end-user’s dream.
Yep Adam, you rock — thanks for the quick fix — this utility is a fundamental part of my hourly workflow!