In my experience, it is the initial session that is the major hurdle. Most gamers are smart enough to see the merits and flaws in a given system, and can determine if the new [free/indy] game will work for them and their troupe. The hard part is getting them into that first game.
There are those players, of course, who will be prejudiced against any new system: reluctance to learn a new system, not wanting to start anew with a less experienced (read: less powerful) character, or always wanting to further the current campaign, regardless of any merits the new system might have.
There are also those players who are almost always willing to try a new game. Just being one they have never played before is a substantial advantage in and of itself. These players tend to be the ones bringing up the new ideas, be they for new campaigns or new free games, and are often willing to run them themselves. As these poor sods are obviously mentally unstable, we can leave them out of the discussion.
One way around this problem would be to issue a starter kit - akin to those product samples White Wolf has made available for the various nWoD settings.
It should be an adventure, some NPCs/interesting locations to spice it up, and a few pre-made characters. Rather than being first level/neonate PCs, start them off with something of an appreciable power level. Let each illustrate a couple of the cool powers that players can aspire to acquire.
Going by Rob's suggestions for RPG organization, including a back cover/blurbs about the game might also help make new players a bit more enthusiastic - though too much makes it sound more like an advertisement.
I'm not sure how we could get user-testimonials on site, and to what degree people would accept them. On one hand, most people seem to get into these games because they join a friends group or other wise by word of mouth/demonstration - so hearing what others have to say might get their attention. But of course random names/e-mail handles on line can be faked and might not be the most credible evidence you should play. Rob's blog is certainly the right way to go, however.
And I'd like to mention I'm in that mentally unstable minority...
Some excellent points here of course. I think that a GM should try to analyse what the group likes and try to play the perfectly matching free rpg. Break them in gently before you get to the wierd stuff