Personally I have to say that compared to my own system, I'm running the GA-990FXA-UD5 that the temps do see a bit high.
Of course, the Northbridge temp will be dependent on what hardware you have installed and I noticed a big drop in temp (over 15C) when I removed one of the Graphic Cards I was using. Also the temp can be affected by the CPU you are using and if it is running at stock or overclocked. Having said that when I had 2x6770ATI cards in crossfire and my 1090T overclocked to 3.8GHz my Northbridge temp maxed out at around 55C. I have just reconfigured my system with one card and reset BIOS to Optimised Defaults and the Northbridge is showing 30C.