Rather than look at the criteria for deletion, the selection process is more important. A category is not approved to become a category unless it has a specific number of questions that need a home-- usually several hundred or more questions. A Community Advisor reviews category suggestions and approves or declines it. Some are held back for future use. However, once a category is created, it is here to stay.
Sadly, the "Harmless Nonsense" subcategory outlived its usefulness - and was being misused - and was therefore deleted.
It is rare that a category is totally deleted, and announcements are not generally made about it. On the few occasions that it does happen, some of the WikiGroups may be asked to help move questions to another area. Overall though, you will probably not receive notification of an upcoming deletion.
No answers can be added to the WikiAnswers Local category.
The supervisors for the 'Questions about WikiAnswers' category are Kamuna and Dino10.
"WikiAnswers Local" is a placeholder category for questions about certain countries. No new questions should be added to the main "WikiAnswers Local" category.
Any questions found to be breaking WikiAnswers' Community Guidelines and Terms and Conditions (see "Related Links" section of this answer) will be deleted or placed into the Catch-All Category. All rules should be followed at all times whilst on WikiAnswers.
That would be WikiAnswers Local.
Questions on WikiAnswers can not be deleted by regular contributors. Supervisors can trash questions into a catchall category, but only advanced supervisors can permanently delete questions off the site.
WikiAnswers has a category called 'Most Amusing Questions Ever Asked on WikiAnswers'. The category is home to many amusing questions that also goes under the category strange, unusual, weird, etc. Below is the link to the category.
Special:Search
There is now a snowmobiling category under Sports.
The "Math" category with eight Supervisors.