Similar to how copyrights are granted without the need to register a claim, a trademark, I believe, can be claimed without registering it. That is the difference between "TM" and "R" (often with a circle around it).
As you can see with the "TM" above the PBooks word on our blog, Savonix has claimed PBooks as a trademark. We also claim a trademark on the PBooks logo. What does this mean? I actually don't know exactly - as I've tried to make abundantly clear, I am not a lawyer. However, from reading the news, I've come across too many stories about open source projects getting bullied by trademark owners to change their names. I also read that someone unaffiliated with linux even registered a claim on it and tried to claim royalties. That is pretty lame in my opinion so I figured it couldn't hurt to document my thoughts and opinions on this subject with respect to PBooks as an open source project.
While I have a little knowledge about copyright, I know less about trademarks, and I know even less about patents, but if you are still curious about my take on how these intellectual property elements are being handled with respect to PBooks, check out PBooks Patents.