Of course there's no totally automatic and reliable system, we're just trying to find something better than manually removing dozens of spam tasks every day.

The past few days we've had a lot of spam on the Blender phabricator instance. These spammers are also assigning tasks to random users, who then get emailed. See here for examples:
https://developer.blender.org/maniphest/query/all/

For the Blender project, I think this is the main recurring issue that we have after using Phabricator for about 6 months now. Regular contributors install arc, but others don't which leads to various problems and confusion.

I'll mention this here in case it's useful to someone. We migrated from Gforge to Phabricator, importing users and tasks. The php scripts for this are not general and contain many project specific tweaks and hacks, but could be useful to someone still, so they are hosted here:
http://developer.blender.org/diffusion/P/browse/blender-migration/migration/

I should clarify, we use Mediawiki to host our developer and user documentation, and probably will not use Phriction. We will also create our own customized "report a bug" page that creates a task, so we need our own links to them. From experience end users need some guidance to create good bug reports and the create task page is too generic.

This is pretty important for us as well. Probably we will add custom content on the home page (with welcome.html or otherwise), so even an empty home page when logged out would be useful to have working.