This is my best walkabout lens. Right weight, brilliant sharpness and versatile enough for all kinds of photography especially travel and portraitures. I sold my Kit lens 17-135mm to get 10-22mm and 15-85mm.
Don't bother with buying a Polariser because the lens is pretty wide and you get uneven effects on the sky. With Photoshop CS5's Adobe Camera Raw, you can easily make your sky blue naturally.
Some people will claim that you need F/2.8. Frankly, I don't in reality. It doesn't make your shoot alot faster in dim lights.
I differ in your view. f2.8 and f5.6 @ 55mm definitely have a great difference. Nonetheless, the 15-85 is a great lens. However, I personally will not pay $1080 for it.