I have one. I needed a new case anyway, so I got Sonata.
It can be considered very quite for office applications, but not "dead" quite for music recording purposes. I would say it is reasonably quite.
Its got some nice features though. Antec power supply has a single variable speed fan - they have removed one PSU fan specificly for this case to reduce noise. This is still the noisiest part of the computer. At the same time, Antec makes very good and stable power supply units, which can realiably handle maximum or even higher load.
Case fan is 12 cm variable speed fan, which is really quite at slow speed, but gets more noticable when the case heats up. There is an option to add a second fan in the front.
A very quite cooler on my Athlon and the fan on the video card are both quiter than PSU and case fans.
Case construstion is very good, it is sturdy and there are no sharp edges inside. Hard drives are mounted on rubber paddings. I am using Seagate Barracuda drives, and do not hear them.
Besides, drives are mounted "sideways", with back side of the drive facing towards you. This makes setting the drives and connecting cables easy and comfortable. Very cool idea.
Overall, it is a very good case, but don't expect not to hear your box working.
