Due to a huge influx of spam across all OBF wikis, we are in the process of locking down new user account creation and adding OpenID logins for the OBF wikis (BioPerl example). User account creation via the old login system will be disabled and OpenID will be the default path for new accounts so users to make wiki changes. This currently appears to have cut the incidence of spam significantly. We will be adding information to the login pages to redirect new users to the new login page.
We also have one wiki (BioLib) that is testing out manual account approval via a wiki bureaucrat in case we have to take more extreme measures, though we would like to leave the barrier to community involvement with projects at the lowest possible level.