It's too quiet, if you ask me. In demanding situations it doesn't put enough air through the system.
You could be right there. They are probably being a bit conservative since the whole G5 thing.
They promoted the iMac G5 as being "whisper quiet" and got slammed with complaints of loud noise.
The iMac G5 was the quietest computer I had ever owned at the time. But, they were apparently noisier than what people expected from a "whisper quiet" computer.
Each subsequent iMac after that had the fans spinning a bit slower. And, I know even the fans in my Mac Mini G4 will ramp-up pretty quick.
I imagine that the fans in the Mac Pro are probably set to keep everything working safely. But, if they ramped-up as fast as those in my Mini do, I'm sure it would keep everything nice and cool. Of course, then we'd likely have more people complaining of noise.
I am not personally using it, but I have heard mention of a tool that allows someone to set their fans higher if they want.
But, I haven't had any heat issues. So, I've just left it alone to manage itself.
Personally, I'm fine with any level of noise that doesn't exceed the noise of your average PC.
But, Apple may be stung from the criticism of it's previous G5 lines. I remember the reviews in the Mac magazines highlighting wind-tunnel effect of the PowerMac G5's.
Perhaps a meeting somewhere in the middle would be best. But, as long as it's reliable, I'm fine.