I was frustrated because the Blosxom wbnotify plugin wouldn't work if you don't have sendmail enabled on your host. I don't have it turned on on the commons webserver, so writeback notifications failed.
After some tweaking (mostly because I can't seem to hit the right keys to save my life today. Come onMotrin, do your stuff), it's working, and happily sending notifications of new writebacks.
If you are in a similar situation, feel free to grab a copy of wbnotify_nosendmail for yourself. It needs some minor configuration before it will work (you need to provide a destination email address, a sender email address, and the location of a machine with SMTP that you want to use).
The current limitation of this setup is that all Blosxom weblogs on a single server (well, sharing a plugins directory, anyway) will send notification to the same account. Not a big deal, since this is the only Blosxom weblog on the server, but it may become a problem...