OS3.9 is far superior to OS3.1 of course. I feel crippled when having to use, or code for, OS3.1... :-(
Anyway, I have compiled a preliminary "Undocumented AmigaOS" document. It is available from my site at http://amigan.1emu.net/releases/
Before anyone yells, I am not necessarily advocating use of any private functions. Still it is interesting reading at least.
@gulliver: are any of these later versions than OS3.9 and/or have functionality not in OS3.9?
@jayminer: are you using BB4 (ie. the faster icon.library)?