Wood
I was reading through the DrunkenBlog archives (as I often do), when I came across the interview with Wil Shipley (which, by the way, is required reading), and noticed this early mockup of Delicious Library:

It reminded me immediately of the most recent MyDreamApp post (which isn’t very recent at all—MyDreamApp is dying) about Cookbook’s interface, which looks something like this:

If you think that an all-wooden interface is a silly idea, that’s because it is. As Wil Shipley puts it:
“At one point we had an interface where we replaced Apple’s brushed-metal with wood, and it looked really amazing but there were some technical issues and we finally decided that, actually, it was cool but it made the interface harder to understand. Sometimes you do stuff that’s just cool for cool’s sake, but you can’t do it if it actually gets in the way of the app’s transparency.”
Let’s hope Austin Sarner or whoever actually ends up implementing the Cookbook interface (if it ever gets made at all) comes to a similar realization.