Rosegarden comes with some documentation in the form of a help system and tooltip help, and you may find the following offerings helpful as well.
MIDI Device Program Maps
For those of you looking to create voice mappings for your own MIDI hardware, here is a mini-HOWTO for creating voice definitions for Rosegarden. You should also check out the ever-growing device library (a snapshot of which is included with each Rosegarden release) to make sure your device hasn't already been mapped.
For anyone interested in helping out with translations, here is a translation mini-HOWTO.
Infrared Remote Controls
A brief description of how to use infrared remote controls with Rosegarden using LIRC.
Developer Documentation for Rosegarden
Automatically generated class hierarchies and extracted code notes can be found on our daily Doxygen dump. Useful for reference and as an introduction to some parts of the code.
There are also some notes to be found in Rosegarden SVN itself.
We now have a Rosegarden Wiki with developer documentation in it.
Bug and RFE Priorities on the SourceForge tracker
If you've submitted a bug report or a feature request, you can use the following tables to determine whether someone has looked at the report yet, and how soon the Rosegarden team expects to do something about the issue or request.