I had retrosigmoid on 5/31/07. My scar is behind my ear - I wear my hair very short and believe it or not, the scar isn't that noticeable since my hair has grown over it. You can just see the tail end of the scar near my ear lobe and unless I point it out to people, most don't see it.
Retrosigmoid gives you the opportunity to try to save the level of hearing you have, but you may end up with a little less hearing, or in some cases (like mine) you may end up with no hearing at all. As with all medical procedures, nothing is guaranteed.
I think a lot depends on the size of your AN. Originally mine was 1.5 cm so they thought the chances of saving my hearing were pretty good. Unfortunately, my AN had grown unexpectedly and was kind of wrapped around the hearing nerve, so in order to get the whole AN they had to sacrifice the hearing nerve. While I would have liked to keep some hearing, the doctor's priority was to get the whole AN and I totally agree with his decision.