The Real World Haskell book is now available for pre-order!
I've just ordered my copy from Amazon UK for £30.99 and it's available from Amazon in the US for $49.99.
I'd like to be able to recommend a canonical "learning Haskell" bookshelf. The slot for an introductory book has been filled by the excellent Programming in Haskell (you can read my review). Judging by the material the Real World Haskell book aims to cover, it looks like it should be a pretty good complement, mostly picking up where Programming in Haskell leaves off and covering the language techniques and tools you need to get started writing serious programs.