I was browsing some old(ish) books in the computer science section of a used bookstore, and there was a popular book on Motif user interface programming. Curious, I started to leaf through it. Then I didn't believe my eyes and went through it more carefully.

About 350 pages. Lots of APIs and descriptions of options and stuff, but exactly one diagram. In the whole book. For me, this pretty much sums up why Unix UIs were so bad.