Hi Ding, when I got my K100D, less than a month after, dust also appeared from the lower right of the LCD. I ignored it, but before my warranty with Sanly's was up, had it cleaned (fixed together with a glitch with manual lenses and hot pixels). When I got it back, the camera was like new again... but then, after a few months, the dust came back. I learned to live with it since then... it's a minor annoyance at best(or worse)...
At least it wasn't like my K10D (sold it already)... while viewing pictures, I thought there was a piece of dust, checked pics again after a few, the piece of dust changed position... then moved! It was an insect living in my LCD! hahaha... I left the camera without lens for about three days, so the bug can get out (I wouldn't want it to die stuck in my LCD!) then all was well...