Ok, I found the code that does the directory listing in mhonarc, by searching for the word "max". Amongst other things, this dug up the comments about the Atari MegaST used for the mhonarc logo. As an Atari 520ST user, it rekindled some nostalgic jealousy.
Anyway, it is get_last_msg_num and just for fun I logged how much time it was spending, using timethis() from the Perl benchmarking module. About two minutes spread over ~300 iterations of mhonarc on real data. Now of course this is not a typical system; I have a large number of files per directory, and am currently using the aufs union mount filesystem. Aufs a little bit slow to return directory listings in such situations. I've bee talking to the aufs folks and there isn't a trivial fix. I think an option for mhonarc to avoid the directory listing would be quite helpful, at least in my situation. -Jeff