The Isis type (and probably Octalink too, since it's the same idea) don't last long at all. Our son who only weighs 130 pounds or so and doesn't abuse equipment seems to get about 3,000 miles out of one. That's not loaded touring either, but he does ride hard and climbs about 4,000 feet per hour. The problem with them is that when they went to the bigger spindle, it didn't leave room inside the BB shell for big-enough ball bearings, and it also put the two sides' bearings too close together so there's a huge load on them from the side-to-side pedaling forces.
The answer to that was the external-bearing BBs, which put the two sides' bearings a lot farther apart and of course also leave a lot more room for adequately sized ball bearings. We have these in a couple of our bikes, one with 7,000 miles and one with nearly 16,000 miles, and they both still feel brand new.
The external-bearing type requires a crankset that has the spindle as an integral part of the right crank arm. Mine requires only an 8mm allen wrench to remove the crankset from the bike and re-install it, and it's so easy that it's almost worth doing it every time I want to clean that part of the bike.
People sometimes think that the external-bearing BBs would give you a wider Q; ie, put the pedals farther apart. This is not the case though. On the left side, the crank arm goes right up against the bearing, not leaving any of the spindle showing. On the right side, the bearing is even outboard of the tiny chainring, and is almost in the plane of my middle chainring.
This message was edited by whittierider on 10-25-08 @ 12:02 PM