I bought this lens a week ago. I was worried about getting a dud after reading reviews on here, and since this is my first non Canon lens. I must say I'm very impressed with the lens so far. Colors are super crisp and sharp, Very little if any distortion on my 10D. Auto focus is a little slower and noisier than my Canon USM lenses, but for half the price of Canon's USM version I can deal with it. 17mm @ F2.8 is much sharper than I expected.
I bought the lens for a trip out west I'm taking next month, and I'm looking forward to getting some good shots of the Vegas strip and of the Utah mountains with it.