For a while I've been meaning to write this, and the article "there's more to Linux than Ubuntu" finally made me do it.
PROBLEM: You keep raving on about the greatness of that mysterious alternative operating system called "Linux", motivating someone to find out more. That someone Googles "linux", ends up at linux.org, clicks "Download" and is then presented with an expansive text beginning with:
Linux, together with a set of GNU programs, is an operating system. That is, Linux is not a single program or a suite of tools. Most "versions" of Linux, known as "distributions", are available to download free of charge.
...and doesn't know what to do.
SOLUTION: When evangelising, don't use the term "Linux", use the name of whatever distribution you're using.
You know those people who keep on whining about you having to use "GNU/Linux" instead of "Linux"? Well, they're stupid, really. I mean, it's not like by using "GNU/Linux" you've named each and every component of your operating system. Heck, if you wanted to do that, you'd end up with names like GNU/Linux/Xfce/Abiword/Gnumeric/Firefox/etc.!
However, by using the name of your distribution, you point to exactly that combination of packages, software availability, and community support that you so appreciate.
For example, I honestly cannot say that I think all Linux distributions are good. I can say, however, how much I appreciate the fact that all Linux distributions are open source. However, if I were to evangelize that, I would use the term "open source".
Bottom line: tell people new to open source about the distribution you'd recommend them, so as to prevent them getting confused. You could consider this dumbing down the masses, however, new users get a lot of information thrown at them, and the most important thing at the beginning is getting them started. They can learn about other distributions later, when they are ready to put some effort into finding the distribution that fits them. You cannot, however, expect them to be able to find that out immediately.