All together my husband and I would have somewhere in the vicinity of 2,500 books, possibly more - and we just did a *huge* cull (have a big pile waiting to be shipped to the Footpath Library).
And, on top of that - I borrow somewhere between five and thirty books from the library each week!
Around 90 or 100 - mostly biological and botanical sciences; field guides; some earth science (major egg head); a few on Tai Chi, Qigong and Acupressure; the life of The Buddha (go figure); a heap of Uni correspondence books and journals and over 100 Shorebird journals.
I now get my bird and shorebird journals electronically.
Current Favourite "Invisble Connections" - awesome book on the shorebirds of the East Asian-Australasian Flyway. Google it, you can even get it in pdf form and it's full of gorgeous photographs. Written in English, Korean and Chinese.