With a couple of the shots, the lighting appeared quite direct and to my eye, a little unflattering. Looking at other shots, some did not have that same look yet flash was still used. I think it's most noticeable on the first shot (top left of your array), where the lighting seems uneven, compared to the shots immediately right or underneath that one, which seem much more evenly lit.
In some of the shots, it seems like the ceiling is too high and too dark for effective bounce flash.
The 60D and 17-55mm make a great combination, I think.