I've been getting kind of interested in this. If you aren't familiar with E6, it is basically a dnd et al mod where you stop leveling up once you hit level 6 and just get more feats, which I think is an elegant way to stop people from becoming world-destroying supermen and women while still letting them not only progress, but have a sense that they are in charge of stuff to some degree. A big problem with a 20-level system is that players are either low level so they feel like they aren't important as far as having an impact on the world, or they are high level and nothing can touch them and they can do whatever they want. E6 makes it so a newbie character can still contribute meaningfully while at the same time a high level character still has to worry about stray arrows and stuff. You can check out a pathfinder-specific resource here:
http://p6codex.com/Does anyone have any experience with this system? It just seems neato.