Note: It seems like many owners experience problems with this headphones. Some seem to have problems for functions these headphones do not have (i.e. sound controller), so I am not sure how justified some reviews are... Overall, none of the problems happened to me. See review for details:
Quality: I bought this headphones in June 2009 at amazon. Since then, I am using them everyday with my iPod touch while commuting to work, traveling, etc. And I use them to call people over Skype with my iPod as well as my MacBook. Usually, I carry my iPod in my trouser pocket with the headphones wrapped around it. Actually, this is the worst thing you can do to headphones. Still, the cable is fully intact, I never lost one of the rubber/silicone pieces - they do not even look 'used'. They are adjustable in size and fit very good and tight in the ear - but never uncomfortable. I never 'lost' one earphone just by gravity. And I do not miss a sound controller. If you want to turn down the music, just grab your iPhone/iPod. That is not a big deal for me.
Sound: Amazing! So much better than the Apple ones I had before. Some people complain about it, but in my opinion they are pure Sennheiser sound quality. If you experience problems with the sound it is most likely the equalizer settings you want to go for. Not the headphones are poor, but even the best headphones do not have a chance with low quality mp3 and wrong settings. Furthermore, they keep the sound around you out of your ears. This is especially great on airplanes, I usually wear them without listening to music for noise reduction. On the other hand, it is not a good idea to wear both earpieces while walking on a sidewalk. You won't hear any bike or car. But I would count this as positive.
Mic: Good for how it is designed. The mic is effectively hanging near your collar. If you are walking, the mic will move - and collect the noise. You won't experience such problems with a classic mobile phone headset. But this is the compromise of having in-ear headphones. Once you sit down and call someone, the sound quality is not worse than with other microphones.
Overall: I think these are real Sennheiser - good sound quality and I never experienced a problem. Now taken into account that a lot of people do rate them badly, sales numbers are low. Hence the big discount. But I do not really complain about this fact, I will buy my girlfriend a pair for her iPod and be happy that I effectively made a steal. Even if the mic can pick up some noise, this is a general problem with the design of this kind of headsets and not MM50ip specific.