^^^^
I've not owned a Shimano internal hub yet, but I've not heard anything about them being fragile, just the opposite. One guy at the LBS is using the Shimano Redline (redband?) series on his downhill bike and has had no problems. I have put more than several miles on Shimano's internal hubs on friends bikes, and I like the feel of the shifter better than any other I've ridden except Rohloff.

I'm running Rohloffs on 2 of my bikes and I've had no problems whatsoever. No adjustments, never lost a chain, skipped a gear, nothing. They have been the best pieces of tech I've ever used on a bicycle. Silky smooth, and maintenance free.
I had a few SRAM hubs on my Giant Lite/Xtracycle, they did not hold up well (both would not stay in the top gears), I swapped to a Sturmey-Archer and it's held up fine.