Hot pixel blues

My new D90 is off to see Nikon to try and remedy its hot pixel blues. I only noticed it when I tried to photograph the sky at night when we had a clear night a few days ago. I don't know now too much about hot pixels but if you have over a certain amount then they will take it to get a new sensor installed. Does anyone know if this is a problem that does get worse over time or is something that stays the same from when the camera was manafactured? I'm a bit pissed off becaused I only had this camera since the beginning of September.