I have 2 rigs running in my office. The specs are as follows:
Rig 1: 4x 5850
Rig 2: 2x 5870, 1x 5850
I have 1 desktop fan blowing on both.
I have 1x extenders and cable ties (zip ties) to space out the cards, it depends on your case.
The 2 5870 have aftermarket HSF on them.
They are quiet, but there's heat and you cannot put it under your desk if you want kids in the future (might be as bad as putting a hot laptop on your lap). ps. I'm not a doctor, but it's up to you.
So how to keep them quiet?
Set them up and don't start mining yet. Try out different levels of the fans on the GPU and once you have decided on a noise level you can accept (I have the sapphire non-ref at 65%, ref at 35%), lock in the fans at that speed. To do that I use cgminer as the mining software with the "--auto-fan --gpu-fan 65" parameter.
I've also setup cgminer with "--auto-gpu" to set the gpu to be down clocked if the temps get too high. I set the range to 500-880mhz. The reference card I have will run at a lower speed, but everything is stable.
I do not keep the air-conditioning on over-night. This will drive up the power bills significantly, so at night, the gpus automatically downclock to about 600mhz. During office hours when the air-conditioning is on, cgminer push them back to 750-880mhz (different for each card, as the card at the end runs cooler).
This is how they look:
Hope this helps.