Amit,
I've checked with some of my contacts within Oracle -- no definite information, but here's what I have:
1) Oracle is working on more comprehensive materials for OTM - however, the primary focus now is on training materials and (pay-for) training classes. You can find more details at:
OU BridgePage
2) If you have access to an OTM installation, the best sources for information are the online help and the "Show Me" simulations. In order to access these, however, you need to have a valid license for OTM or work for a company that does.
3) I wouldn't hold my breath on more comprehensive documentation -- it's a long process and OTM is a fairly young product (less than 7 years from the first production release).
Your best sources for learning are going to be hands-on experience and online communities like these forums and the OTM SIG.
Thanks!
--Chris