i built a commuter bike for my girlfriend with full ultegra 6500 groupset and after over a year of daily use there are no problems with the groupset whatsoever. the only issue i can recall is that crank bolt was loosening from time to time but after tightening it few times, is all ok now. as someone mentioned before there are v1 and v2 versions and they are not compatible. the bb reviews i recall, mention that 105/ultegra octalink v1 are bullet proof unlike dura ace and you can still buy brand new 105 bb in many shops.