The World category has the most sites and also the most unreviewed sites. 

These categories have more unreviewed sites than listed sites: Adult, Computers, Business, Shopping and Health.  This is probably because these categories are the most likely to be spammed

The categories have the most unreviewed sites (listed in order) #1 World, #2 Business, #3 Regional, #4 Computers  and #5 Arts.  These categories have a lack of editors or high spam or both.

These categories have the most sites (listed in order) #1 World, #2 Regional, #3 Arts, #4  Society and #5 Business.  Kudos to the human DMOZ editors in these categories. 

DMOZ is a huge project and not everything is perfect as I have mentioned earlier.  Before you start complaining about it ask yourself if you have helped the situation or hurt it.  You can help by volunteering.  You can hurt it by submitting your site multiple times with keyword stuffed descriptions.  This increases the work that the human volunteers need to do.  The more work means the bigger the backlog.