When you put many new pictures in folders, (may be hundreds, not yet counted) the Finder crash, and reboot. So you lost all your finder settings.
It was the same under Snow Leopard. The only progress under Lion is, after crash, most icon still appear correct (512 pixels, but not all), under SnowLeopard most icon appeared 32x32 pixels !
Most icon come back to correct (not all) after close and reopen session. Restart seem more efficient... sometimes...
So I agree withe "unpeople" there is a real coding problem !
Come on Apple The new spluttered king of the desktop is just pathetic !