Shirley has always and will always be a very dated and old fashioned (and not in a good way) name.
I also think of it as a male name, as there was a male television personality as i was growing up named this. Also, for some reason I associate this name with a screeching sound, I'm not sure why, I wish I could explain it!
I don't think it will ever be really popular - its far too old fashioned for most people to even consider, especially given the trend for tryndified names at present. Unless of course Sherlee became popular :P