An excellent post was made at WebmasterWorld under the title of YP Category Usage Percentages by a member named inbound. I am going to quote the whole post right here.
I just completed some research based on a variety of industry data, here are my rough figures for overall offline YP category use. It should not be a shock to many of you but I thought it might help some people in search of general data. Take your pick on the number of lookups, 15 Billion seems a nice round figure for the year. % - Category
15.6 - Health 14.2 - Food 13.8 - Automobiles 10.2 - Shopping (Consumer) 7.1 - Construction 4.2 - Supplies (Business) 3.6 - Finance & Insurance 3.5 - Home & Garden 3.4 - Professionals 3.2 - Entertainment 2.9 - Travel 2.5 - Beauty 2.2 - Pets 1.9 - Government 1.8 - Education 1.5 - Repairs 1.4 - Transport & Haulage 1.1 - Property & Real Estate 1.0 - Utilities & Fuel 1.0 - Domestic Cleaning 0.7 - Business Services 0.6 - Media 0.5 - Communication 0.4 - Weddings 0.4 - Motorcycles 0.4 - Employment 0.3 - Boats 0.3 - Agriculture 0.3 - Small Package Delivery
Moderator of that forum, Chicago, then posted some other resources, including "Top Ten" Category Searches in Print and Internet Yellow Pages Reveal What Consumers Want (PDF) by the Yellow Pages Association.
Forum discussion at WebmasterWorld.