Just a little buglet...
mx1 329% mhonarc -afs -outdir ./oct99 .mbox/oct99
ERROR: "oct99" is not readable
mx1 330% ls -ld oct99
drwx------ 2 80 202 2048 Oct 21 15:22 oct99
mx1 331% touch oct99/hi ; rm oct99/hi
mx1 332% chmod a+rwx oct99
mx1 333% mhonarc -afs -outdir ./oct99 .mbox/oct99
Converting messages to ./oct99
Reading .mbox/oct99 .........
Looks like -afs doesn't actually ignore the permissions in the directory,
even though I can write/delete files from it. This may only be the case
when it's not in -add mode, though. I haven't tested it any further.