I think I'd want a private library like George Lucas's at Skywalker Ranch in Marin County. It appears to be modeled after the 1938 library at Chateau de Groussay, but with warmer colors and a 40' diameter stained glass dome. It's amazing what a 40' stained glass dome can do to spruce up any room. You should try it the next time you're redecorating.
You can browse through Truly Grand Home Libraries here. Interestingly, there are almost no pictures available on the Internet of the library that Bill Gates built his librarian mother.
The two guys on the list who definitely use their huge personal libraries, Larry McMurtry and Umberto Eco, go for the Ikea white pressed wood shelf look. You can't afford a George Lucas-style library from selling books, even as many as McMurtry and Eco have.