Version:            (using KDE 4.2.3)
OS:                Linux
Installed from:    Unlisted Binary Package

When in menu subcategory there is only one or two items there's no need to show subcategory and one or two items inside. It's better to show these menu entries directly in their category, without subcategories.

There's also no need to show subcategories when there are only apps from one subcategory. 

Example: there are only two programs in 'education': marble and kmplot. It's better to click education->kmplot than education->math->kmplot, same for marble.

Another example: there's lot of programs in education->geography and only kmplot in education->kmplot. It's better to show kmplot directly in 'education' and group geography items, but in this case I would consider not using subcategries at all.

Summing up in most cases there's no need to use subcategories. They make choosing programs easier only if there's lot of programs in the same category. I would limit using them to cases when there are more than 10 items in one category and minimum 4 of them from one subcategory.