I wouldn't go off-topic but I found the following very interesting: <a href="http://thenextweb.com/apps/2010/12/27/in-2010-chromes-rise-was-firefoxs-loss/">In 2010 Chrome’s rise was Firefox’s loss</a>
IMHO if those stats are saying the truth, the decision of removing h264 support from chrome will probably cause even more users to move from firefox to chromium ... but we won't see many IE or Safari users going to chrome
I used to go through one of the metaphors you've mentioned. Specifically the "car with the hood welded shut" worked well in many occasions. But it also leaves few questions unanswered.
So, lastly I changed my approach and started using the definition of free software which is very well written on the <a href="http://www.gnu.org/philosophy/free-sw.html">GNU</a> website.
Wording accurately the sentences is very important; this is the piece I usually start with:
<cite>Free software is a matter of the users' freedom to run, copy, distribute, study, change and improve the software. “Free software” is a matter of liberty, not price. To understand the concept, you should think of “free” as in “free speech,” not as in “free beer.”</cite>
I also add a short description of the four essential freedoms and then use Linux as practical (and well known) example of how those have been successfully applied to build an operating system.
I wouldn't go off-topic but I found the following very interesting: <a href="http://thenextweb.com/apps/2010/12/27/in-2010-chromes-rise-was-firefoxs-loss/">In 2010 Chrome’s rise was Firefox’s loss</a>
IMHO if those stats are saying the truth, the decision of removing h264 support from chrome will probably cause even more users to move from firefox to chromium ... but we won't see many IE or Safari users going to chrome