NTIFS vs DDK? (documents)

If you want to learn what really windows is all about and how it works internally, DDK's documentations are surely a must read item. However, DDK's documents are not particularly suitable as the first reference as they are too short of explanaitions on WHYs and WHAT-IFs. A better idea is to start reading some books like "windows driver model" or other books about writing device drivers and use DDK as a reference material. You can find these books and more on the FTP.
IFS, however, is a different beast. There you don't find any usefull info but just for writing files-systems. I think this is a rather very very specialized topic and amongst all other things you should learn about the low-level structure of the windows, it is one of the less important topics unless you want to write a complete new files system or port something from say, Linux world to the winodws. But for normal (?) hackers, I think there is a very small need for the IFS kit.