PSP-3000 scanlines a hardware feature; no fix planned
The worst news is that there's no fix. "Since this is caused by hardware characteristics, there is no plan to fix it with system software update." Looks like it's here to stay. We're still waiting on a statement from SCEA but, from the looks of it, they won't have much new to add.
Update: SCEA response, after the break.
"On some occasions, scan lines may appear on scenes where brightness changes drastically, due to the hardware features of the new LCD device on PSP-3000. Installed with this new LCD device, PSP-3000 offers more natural and vibrant colors on its screen, but the scan lines have come out to be more visible as a result of improving response time to alleviate the afterimages on PSP-3000. Since this is due to hardware specification, there are no plans for a system software update concerning this issue."