I have the curve for mine set such that they stay around 800 RPM from system idle through moderate activity, and I don't hear them at that speed. When I am gaming or performing some other extremely demanding computational task, they kick up higher (automatically), but are pretty much drowned out by my GPU (or CPU) fans...which are also automatically controlled based on load/temp.
Personally, I just don't want to be screwing with knobs all of the time...and given that most folks have a CPU cooler and GPU cooler with fans that are dynamically controlled based on temperature, I just don't get why they want to take on manual control of the case fans. Oh well, to each his own.
Yeah I used to let the mobo dynamically control the fan speed, bet eventually I ran out of fan headers. Also, I probably have 4 different fan models. What I was most concerned with is speed at idle, but it seemed just about impossible to get them all to idle at the ideal speed of 600-700. Some would be at 1000 and some at 500. The controller allowed me to further fine tune it. If I wanted to I could still hook 1 or 2 fans up to have them automatically changed and it would work well, but at the moment I am happy with it now.