I hit 38°C yesterday, these boards seem to run very warm.
The VRM and sensor (temp sensor that give the m/board reading) are, as far as I can determine, at the lower end of the memory slots partially concealed by the graphics card.
I believe the heat radiated from the graphics card is partially responsible for this "inflated??" reading. I have 40mm fans on both my Northbridge and Southbridge so I know for a fact that they are not overheating.
I did contact Asus Technical support concerning this and may as well not have bothered with the responses I received. If you have good air flow through your case your should be fine, as stated above, the board max temp is ~45°C so until you reach that there's no problem imo.
Here's a pic of the VRM and sensor on the P5K, I've yet to strip my 8800 out to confirm the exact location of it on the P5E3 but I would suggest that it is at the bottom of the ram slots. You could try directing a fan at this location, I have one stuck to the m/board tray at the top of the ram slots that blows "down" the length of the modules towards the sensors "general area".