Stefan Krause wrote a university assignemnt about NMRShiftDB (in German). It's available here.
You can also view the api doc for nmrshiftdb2 at http://nmrshiftdb2.sourceforge.net/api/.
The current ER diagram of the nmrshiftdb2 database is also available here.
There is an nmrshiftdb2 administrators' guide and a developers' guide. Various topics are also discussed in the nmrshiftdb2 wiki.
There have been two papers published about NMRShiftDB in the Journal of Chemical Information and Computer Sciences. Read it here and here.