I organize events and need a solution to bind all kinds of content to specific events.
Tags should be the solution, but turn out to be completely useless across different custom post types and across different blogs/sites in a multisite installation.
I think categories are actually more flexible, but using them this way really goes against their original purpose.
There are a few sitewide tags plugins that are really just window dressing and workarounds. But because they "exist" there will never be a real solution.
Does anyone have a real solution for true installation-wide tags? Can Automattic please fix this in the core?