I have one also (based partly on Kelly's evaluation and partly on my excelent prior Sigma experience). I love the lens - it's much smaller and lighter than my old Sigma 28-200, takes very sharp pics, and focuses fast. It is a bit noisier than other Sigma lenses or Canon lenses when focusing.
I haven't been to WDW since I bought the 18-125, and I'm really eager to get there and try it out!