How hot is too hot for Asus p5Wdh deluxe?

That seems fine w/ air cooling. I use water w/ the same board, but i have the E6400 and my board is around the same temp as yours, although my processor is about 25c. All seems well with this mobo.
 
Mine runs at the same.

What case and how much cooling do you have? I have a Lian Li PC-60 with four case fans (two in / two out) and everything seems fine except the mobo temp. It doesn't seem particularly hot in there either.

Damn thin better not go pop...

Digibit