Practical solution to get an overview of input formats in use I'd like to clean up unused text formats on some D7 sites. So I need to know which formats are not used. I tried using VBO for this, but there is no field Content: Text format I can add there.

What's a good way to get an overview of formats in use? I'd be ok with using drush for this and I can settle with just knowing the nodes and blocks that use a specific format (ignoring other places like views headers).

I'm not looking for a generic answer like "it's stored in these and these database tables". I'm looking for a practical solution that I can use on many Drupal sites.
This is stored on a per-field basis.  

Take a look at your database,  any field_data_*  table.  In those tables, the field_X_format column will contain the input format.