I'm experimenting with using WordPress as an archiver/CMS for various mailing lists. I'm running an import of the archives of the list using a custom PERL (*cough*) script that directly puts them in to the db right now.
I'm currently at 51,000+ posts and looking at probably 70,000+ for this list (1992-present). WordPress does an excellent job of handling dates before it was born :)
So I'm curious, anyone out there running WordPress with 100,000+ posts? I'm contemplating using it as a knowledge management system for various email lists for searchability and RSS output (eventually to Urchin for intelligence).