I have a bit of an IKEA fetish, myself (as evidenced by my using your comment as an excuse to go look at the Leksvik), but it's mostly limited to online window shopping since the store is a bit far and the biggest thing I've wanted to lug back was a POANG chair. I like the Billy, and I like the red BERGSBO bookcase with glass doors too. That's probably even less grown-up (I think it might subconsciously remind me of kindergarten with the bright colored big cubicles)! Anyway, your cats might like this http://ikeahacker.blogspot.com/2007/04/stairway-to-cat-heaven.html if you decide to reclaim your bookshelf.