Hi all - I've asked my IP attorney to provide further detail which I'll share but essentially and to refer to an authoritative source, refer to the first 3 paragraphs here:http://www.fr.com/prior-user-vs-federal-registrant--whose-mark-is-it-anyway1/
Note, when we filed for BitShares last year, the US Patent and Trademark Office (USPTO) used our own postings (on domains that we owned no less!) to initially make reference that the term was already out for public use and could not be trademarked. We pursued that successfully and yet they added that the term was 'too descriptive'.
For the uninitiated "Too Descriptive" means:
A trademark that is overly descriptive and lacks secondary meaning is considered to be invalid. A mark is descriptive if it conveys an immediate idea of the ingredients, qualities or characteristics of the goods or services. This is because it would be unfair to allow a firm to prevent its competitors from informing consumers about the attributes of the competitor's brands by obtaining sole trademark rights to the descriptive terms. This also ensures the freedom of the public to use the language involved, without the possibility of infringement suits by the registrant against others who use the mark to advertise or describe their own products or services. If a firm does use a generic or descriptive term as a trademark, this makes it difficult for competitors to market their own brands of the same product or service.