It will not effect the sound wearing them either way (over the ear or down) they'll sound the same providing you're getting a correct seal. The only problem you'll run into has been mentioned, comfort issues as some IEM are simply not designed to be worn down. To be honest when I first joined I was very hesitant about wearing an IEM over the ear it was completely foreign to me and I didn't want to know about it, feeling embarrassed, comfort, what people would think. Though after you do so, there's honestly no problems, they're just as comfortable and actually emit less cable noise due to the cable canceling at the ear. In a nut shell a large majority of high end IEM's are designed to be worn this way, so being blunt without meaning any offence the morale of this story is 'get used to it'
Edited by H20Fidelity - 11/25/13 at 12:23am
Here's a picture of GR07 being worn down, it works however, not the most confident. the best advice I can give you is don't be affraid to wear an IEM over the ear, it's really no different in looks and who cares if anyone says anything?