This is what happens to a wooden bookcase placed under an aircon over 8 years. The wood is plumped out from being waterlogged and has started to leak in ugly streaks.
I moved into my sister's room after she got married and kept her bookcase as is. But, since the wood has started to give way and the books get drenched from aircon condensation, I had to clear it out. All our old textbooks and yearbooks go into storage, storybooks go to the kids and cookbooks to the cabinet near the kitchen. I moved my books into the custom shelf on my table and everything fits in perfectly - craft books, books that I received as gifts and storybooks that I plan on reading soon.