I don't have that particular board but the two case fans connected to my DG45ID both run between 580 - 620 RPM (the CPU fan runs at around 1135 RPM) and it seems the trend is that newer motherboards only speed up the fans when the cooling is actually needed ie when things start to get too warm. As long as Intel Desktop Utilities says your temperatures are all in order, enjoy the silence!
That makes sense. Compared to the temperature I got when I had a BadAxe2 and an OC'ed Q6600, it's not even warm with the DH67BL + i5 2500. Now that my PC is so quiet, I'm sort of annoyed by HDD noise, which I hardly heard before! I might get SSDs...