I would have gone IGH long ago except for the horizontal dropout (rare) or chain tensioner (klugy) requirement.
When I do eventually do it though, I'll probably get one of the new NuVinci hubs. Infinite gears! The only problem is the one guy that I know that has tried it says that after 5 minutes with it, you'll think all other shifting systems suck.
__________________
Work: the 8 hours that separates bike rides.