I must be honest I have never read the manual for my Nikon D90, just flicked through the quick guide when I purchased my camera last June and read D90 for Dummies which helped me a lot.
On reading my manual for the first time, with my D90 at hand, to try all the settings and functions, I found it easier to understand the manual. There are a couple of areas that I will have to work through again and practice to get a better understanding of. It also helped having a photographer friend who has helped explain certain bits I was unsure of. Overall the manual is well worth reading.