I loved that lens when I had it, but I returned it after it started accumulating dust particles at an alarming rate. My second copy started accumulating dust after only a few days! I do agree that a few dust particles will have no effect on image quality, but I figured at the rate it was collecting dust, that it would eventually affect image quality.
I also checked out 2 other copies of 17-55mm belonging to friends, and they also have dust in them, so 4 out of 4 copies that I have seen have dust accumulation issues.
P.S. By the way, I expect pretty much all non-sealed lenses, even primes, to eventually gather some dust inside, but my 17-55mm copies were collecting dust at unacceptable rate...