In the old forum we used a structure of
Category (SQL Server version)
-- Forum (TSQL, replication, etc.)
This one does nested categories rather than forums inside categories.
We really have two options here. The first is a category for each version of SQL Server and then dynamically creating tags for various topics: TSQL, admin, replication, ssrs, ssas, etc. That's the way it is now.
This will give us a few high level categories but users will certainly forgot to tag posts. Or not know to.
The second option is categories based on TSQL, admin, ssas, ssrs, high availability, etc. That would lead to a lot more categories. We could then use tags for the version of SQL Server. Many posts wouldn't need to be tagged. For example, a generic question on SELECT probably wouldn't need the version.
I'm really torn on the best way to do this.
(And I'm really afraid we may not know the answer until we've been doing it for a while.)