I felt so loved as a customer of No Starch Press. They sent me the book, let me download the ebook in three free formats (no DRM), plus I got a bunch of freebie stickers.
The book itself is also quite remarkable to me in that I can read it and understand Haskell without needing a computer. I am used to reading mathematics books, and while I don't think Haskell is a programming language for all mathematicians as is so often advertised, the language does have a certain appeal to it in that you can treat its programs as abstract exercises that you can do independently of a machine. The statelessness of the whole thing doesn't need me typing stuff into a machine to see what a particular line of code. This makes it great for offline reading, away from the computer.
So yeah, get the treeware version. Support your favourite authors. :-)