First of all, the sound quality on these headphones is significantly better than the standard iPod set. The treble is very good, the bass is good but could do with a bit more punch on bassier tracks, but for most genres of music the Sony headphones create a very enjoyable sound. This is further benefitted from the "in ear" design which cuts down background noise well. The volume is also better, but that is perhaps in no small part due to the iPod earphones being so quiet rather than the Sony ones being particularly loud.
The set comes with a choice of ear plugs to fit most sizes of ears, but my problem was that I was "between sizes" meaning that one was a little too tight to fit in comfortably, and the other requires constant pushing in when listening to the iPod on the go, especially running.
The quality of the set seems very solid, and should last longer than the iPod set. For the money, this set provides great value for money too.