I have had my computer for 1 1/2 year now and ive been very happy with it. the only thing that annoyed me was the noice. I't sounded like a airplane in the corner, and all i wanted was a computer that was silent.
6 days ago i decided to buy the Noctua nh-u12p fan and heatsink + 4 extra silent fan's. It was not that difficult to install it, the only thing that could be difficult for some people is that you have to take out the motherboard to mount the bracket's.
So far I'm very happy with it, the core temperature is around 36 - 40 'C on 0 - 10 % load and 48 - 52 'C on 50 - 80 % load.
And when im sitting next to it i can bearly hear it.