Ask HN: Experience Report on Sussman's "Software Design for Flexibility"?

I'm interested in hearing from anyone who has experimented with, or implemented play/production systems using strategies/techniques/concepts from the book.

Which techniques did you use? Which did you not?

How was the development experience different?

Did you find them useful?

What took the longest to wrap your head around/get used to?

How "total" was your use of techniques throughout development: were you writing a bunch of combinators from square one, or did you pick and choose specific instances to use ideas from the book?

Would appreciate indication if the project in question was a personal side-project, or a production system with other developers involved. Any other thoughts and comments are welcome as well.