From Mark W's suggestions, I almost have a solution to my problem. I have too many rows and columns for a single pivot table.

I have 400 categories which I'd like to use as column headings. I have tons of clients that I'd like to use in the rows (prob about 2000). I only care about data for the 300 largest ones.

I'm thinking of breaking the categories into two groups and putting a group identifier into another column and using it to determine separate pages of the pivot table. I'm concerned that I will run into a problem with the tables still being too big and having too many cells. Suggestions?