mod_auth_mysql patched to work with phpass
Do you use mod_auth_mysql, the Apache module that allows authentication of users to happen through a MySQL database?
With this, you can now have single sign on (SSO), with authentication against a WordPress blog (or bbPress forum). Note that WordPress (in 2.5 and later), doesn’t use MD5 hashes to store passwords any longer; instead they are salted and hashed with the phpass library. The Automattic folk use this to provide SSO for Trac and Subversion.