Yeah - I had to swap out a Nextel 7520 several times before I got a decent one. Not due to dust but other problems. I'm not sure who is in charge of quality control at RIM or Nextel or both that just sends the refurb unit right back out without really checking it out.
Crap, I'm looking to dump my old 7100T and wanted to clean it up before giving it away. I was able to take care of all the scratches on the front using a couple abrasive applicants, but this dust behind the front screen is odd. Not quite sure how to remove it.