Personally I still buy PDFs, however I do not buy them unless I have access to either a preview of said PDF, access to other material from said publisher or author, or good recomendations from trusted sources.
If I'm buying a $5.00 PDF I only need to find about 3 - 5 pages useful to justify the purchase. Whereas if I'm spending 20 - 30 dollars on a book I've got to find most of the book useful to justify the expense, because not only does it cost more but it takes up shelf space that I'm already out of.
This being the case I have PDFs that cover thousands of topics. However, I have print products that cover core rules, a couple settings (2), dungeon building, traps and such, a couple different game systems, a couple magic systems and that is all.