Well I'm not a lawyer, but let me pipe up anyway. :^) Re: /m13
Common words and phrases can be trademarked when they are
associated with a product that someone is using selling or
profiting from. Trademarks for non-commercial purposes are
more difficult to obtain. Non-profits can do it, but last I
checked, I can't get a trademark (or a servicemark) on my
nickname, "Eli the Bearded" -- I do not use it to sell anything
or to promote something that earns me money. (Servicemarks are
like trademarks, but apply to for-sale services.)

Part of trademark law requires only that there be no confusion
in the market for the product associated with the mark. So
Unix can be a trademark for an operating system
seperately from being a trademark for diapers because
it is very unlikely anyone would confuse them.

The disclaimer on the fairandbalanced.info site talks about
copyright, which is a whole different ball of wax. US Patent
and trademark info is at www.uspto.gov, while copyright info
is at www.copyright.gov (a Library of Congress site). This
copyright FAQ (there are several FAQ lists) is relevant:

http://www.copyright.gov/help/faq/faq-protect.html

Copyright can give you much stronger protection, but is not
feasable to use on small text works. But you can copyright
the editing, selecting, and non-alphabetical sorting of
things. And copyright can allow you (excluding 'fair use' usage)
to prevent any usage, even in non-confusing contexts.

The thing about knock-offs, is they can be allowed. Consider
how many dictionaries are available. Or how many companies
make street maps. It is just that the names and logos cannot
be confusingly similar (trademark law) and the contents cannot
be exact copies (copyright law).