For those who are still having longer boot times on the rmbp (30+ seconds) I found that enabling automatic log in cuts the time to about 9 seconds. Just thought I'd let you know so you don't get the same frustration I had with it.
Yeah I did this... And my rMBP Literly turns on from black screen to online everything loaded in about 9-10 seconds! Unbelievable!! Love it except it makes me rethink why I need an iPad now haha