Most users of multisite or custom post types will need ways to connect content from different blogs or different post types.
Tags would be the obvious instrument to achieve this. Unfortunately blogs and post types all have their own separate tags.
This plugin is supposedly the solution, but it just creates a new blog, causing all kinds of other issues.
Please Automattic, fix this in the core! If you want to be a full CMS, not just blogging software, you need this solved.