Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Answer: As dumb as necessary.
Let's rephrase: How technically sophisticated should GNU/Linux users have to be? How knowledgeable should any computer user have to be? The answer to that, of course, ranges from "very" to "not very." We need to get past the name-calling of clueless newbie and sneering elitist, and understand that there are going to be varying levels of ability in any community, including the one made up of people interested in using free software. From there, I suggest it is critically important that we expand the size of the the free software community. That means dealing with more "dumb" people.
I've been thinking about this in the aftermath of Steve Goodwin's post last week and the resulting discussion. The commenters take up familiar battle positions. Newbies suck because they can't figure it out and can't be bothered to learn how to figure it out. GNU/Linux users suck because they are snobs and the system is hard to use and the combination of the two is why we'll never take over the desktop.