Category Counts
You can click Show Counts from the Edit menu or click the
Show Category Counts button on the toolbar button.
This will show 
- the total number of categories in each dimension
These appear within parentheses next to each dimension name on the dimension line.
- the number of other categories in each dimension; that is, drill
categories, root categories, special categories, and categories in
subdimensions
These appear within parentheses, below the dimension names in the dimension line
- the number of regular categories in each level
These appear within parentheses following each level name.