A couple months after I got the Samsung SGH-T809/D820 I started having dust problems with the screen. The first solution was easy enough - pull up the screen and clean it. Unfortunately, this didn't last.
Twice now I've taken my T809/D820 apart to clean the dust. This time I put a hefty dose of RTV silicone where I think the dust is entering at; if it still gets dusty this time, I know I need to tackle the problem from a different direction.