Trademark lawyer Anthony Tambourino noted the Red Hat free-distribution trademark story below and writes:

There are a couple of issues to watch out for when representing an “open source” client. 
First, be clear who the owner of the trademark is.  There are thousands (literally) of open source projects (See SourceForge).  Often, a half-dozen programmers (a/k/a “maintainers”) work on these “projects” for free.  Very few, if any, of these projects have a formal corporate structure (The Mozilla Foundation and The Apache Software Foundation being notable exceptions).  You will probably need to discuss with the client the need for a corporate structure before talking to them about trademarks.  Programmers come and go, especially in the smaller projects, so it is critical to set-up a structure that keeps the rights with the original project.
Second, there are always 2(d) (likelihood of confusion) issues.  Mozilla, who you would think has attorneys on top of these things, had to change the names of two of its browsers.  Firefox early on was called Firebird and Mozilla’s Mac-only browser, Camino, was originally named Chimera, both changed due to trademark issues,  Also, look out for 2(e)(1) descriptiveness issues.  You will often see projects named something like FREEVIEW for an open source all-purpose image reader.
Lastly, there are dilution issues.  I think that is why we are seeing Red Hat’s sudden strict stance regarding use of its trademark. It protects Red Hat from poorly maintained and insecure distributions using the Red Hat name (and let’s face it, open source software’s claim to fame is its security (especially vis-a-vis Microsoft)).  However, it also permits Red Hat to funnel consumers towards its own distro.  If a consumer wants a Red Hat distro, how does the consumer know what he or she is getting if the company can’t say “Brand X, a Red Hat-based Linux distribution”? 
The GPL (General Public License) covers no activities other than copying, distribution and modification (see Paragraph 0 of GPL).  The stance that Red Hat has taken is interesting, as I see it, because it shows how trademark infringement and a copyright “right of attribution” can be at odds.  While I think it is clear that Brand X using the Red Hat trademarks all over its own advertising is infringement, I don’t know if that necessarily goes so far as to permit Red Hat to enjoin Brand X from stating that it is a “Red Hat based distro”.  Perhaps Red Hat lawyers will start negotiating with individual Red Hat-based vendors regarding the “right of attribution”.