Last year I was teamed up with Miloš Šilhánek to create a NetBeans Platform book. Due to situations that don't matter anymore, the book was dropped when it was already done.
So... we decided to provide it to the community: http://wiki.netbeans.org/BookNBPlatformCookbook
Content is based on NetBeans 6.8 - 7.0 and will be updated as needed.
It would be great to get your contributions! It is still a work in process but it should be 90% still valid.
Hope you like it!