Haha, yeah and you probably won't be able to have kids either. Simon, feedback from the headphones shouldn't be a problem even using a mic like that. Your vocals should drownd out the headphones rather easily if your headphones aren't up to loud. :) You will always hear it alittle bit when your not singing; to get rid of it just apply some noise gate. Make sure your threshold is 'just' cutting out the headphones or any other unwanted background noise(usually -15 to -20db, also fast attack and slow decay). Too much threshold and you'll effect the vocals which you don't want to do. If your still picking up the headphones at -15db , you probably got them up too loud.

The volume of the headphones should be at a comfortable volume. I know alot of people always want to turn it up above that, and believe it or not it will effect your singing. Too loud and it will force you to sing louder and as a result you'll usually be sharp. Too low and you'll be flat. You sing better when you sing at the volume you also clearly speak at. Your vocals will also be more powerful too, since they'll be clearer and more present. Singing louder makes you sing sharp, which is singing out of tune, which makes you disappear in the music. Samething will happen if you sing too low.