You can add more than one category at a time. For example, clicking the "Add categories" button, adding in a category, typing it in, hitting "Enter," then just adding another one next to it then clicking the edit button. It saves a lot of time, and more work can be done in a fewer number of edits.
And, are you adding your typical user page for this wiki :)?
Oh, I didn't notice that. Normally, when I add categories, I only type some character, and some suggestions will be showed (for example, I type "3-", after a second, the screen shows "3-Depth levels"), I click on it and click Save.