I just downloaded the latest alpha, imported my kGTD items and got started. There's a little mini-manual somewhere, but I seem to have deleted my copy, and I can't figure out where I got it.
Ah - it's on the wiki:
http://scotaganda.com/omni/index.php?title=Main_Page
I got some information from reading this forum as to what was possible, then I just tried things out in OF. I'm sure I'm just scratching the surface, but I'm learning.
Just make lots of backups - although the software is very stable. I've had a couple of scares, but haven't lost anything major.