For the overall design principles, see

* http://ww.telent.net/diary/The_Programmer_s_Guide_to_Financial_Book_keeping__Part_I

For the current state of implementation (features done and features
planned), run "rake spec"

I'm still learning my way around a lot of the libraries and stuff, so 
if you see things that aren't idiomatic Ruby or aren't the best way of
working generally, it's more likely to be ignorance than deliberate.
Feedback welcome.