Having seen many portrait shots online taken using the 17-55IS. I have come to a conclusion that the 17-55IS lens is a good lens but just not good enough. True enough that it's a versatile lens but it's not a good one for specific purposes. Since you like portraiture, I suggest you look into replacing the lens with either the 24-105 or the 24-70. The bokeh is sweeter for these 2 lenses.
Well..the 24-70 or maybe the 24-105 will be coming in the near future, when I get my FF body

As for now, the 17-55 is my workhorse as I need the wide and tele ends of it to cover wedding.