When to dresses different people have ways, some wear an attachment for the pump that clips to the bra, others tuck it in their bra, or sew a baby sock inside the dress to make a pouch, I actually wear dresses or skirts only jeans or trousers... So wear mine clipped to my waist band..
Often or not it's in plain view, but in the 4 years I've been pumping, nobody's taken any notice of it, never been asked what it is as people assume it's either a MP3 player or a mobile phone clipped to my waistband..
Going back to dresses etc, I would look at the pumps that have remote's to them like the Roche Combo which has the remote and Blood Glucose meter combined in one unit, then you don't have to worry about having to get at your pump to do a bolus or corrections..