the rubber ear pads would fall off. I was continually looking for the pads. You can buy spares, but only in packs of 5 pairs for $25 from specified Sennheiser dealers. Do poor design that they could fall off.
the strain relief on the connector didn't work. eventually, the cable split under the strain relief. A 'sports' model designed with specific iPhone features should be able to withstand being in a pocket.
the screwheads rusted. They are a 'sports' model designed to withstand sweat. Ya coulda used some stainless steel screws guys...
One of the speakers started rattling. I don't really listed to load music, but they started rattling and the audio quality deteriorated.
So they did me great for the first year and I loved them at first. But they really were not durable enough. It seems that Sennheiser have now replaced the model with a new PMX685i.