Just thought I'd report my experience. I am in the UK and bought a handset (not locked) and I noticed the dust issue after about 2 months with my handset. I put up with it because I did not want to loose my new Sensation!
It's now about 10 mths old and the dust had gradually got slightly worse (RHS middle) so I contacted HTC UK. The service was absolutely faultless!
I called the UK contact and the handset was collected by UPS on Tuesday - that was 3.5 days ago and this morning I received my now perfect handset back.
I have checked and it's the same Serial number and IMEI - but looks like new. The letter that came with it lists all the parts used (see image below).
Of course I need to unlock the handset but it has been returned updated and after a 19 Mb update just now (from HTC) it now has Android 4.03 and Sense 3.6.
That's all from me - only time will tell whether the dust returns and HTC have actually fixed the screen gap issue - if not then I have more than a year more left of my 2 year HTC UK warranty to rely upon.
BTW: I forgot to add that I returned the rooted handset with Android Revolution and super CID etc all on the handset. I made no effort to remove it as I reasoned that HTC were being asked to replace what was a faulty screen and the issue did not relate to software in any way. You should know that when you return a handset in the UK it goes to an HTC agent (Regenersis PLC, Cambridge) and they state that they will wipe the handset of all data as it would be returned with a new software (ROM etc) load. Clearly this HTC update while being 'fixed' was not affected by the root I had done - I do not know if it is still rooted....