I use 5 of these fans in my CM590 (with window) casing (2x top exhaust, 1x rear exhaust, 1x side panel intake, 1x HD cage intake). Fan speed controlled automatically by mobo (temp controlled) and Aerocool fan controller. 5 fans running at the same time is quite loud. Not the high-pitched whine common with high-speed Delta fans, but just a general loudness. Luckily for me that rig sits in a spare room with another rig (which is very silent due to silent fans + sound proofing materials). So I am rarely in that room. The rigs run 24/7 (folding@home, and DVD ripping from time to time).

Due to the high volume from many fans, I've decided to only use 1 or 2 of them (for intake) in my 2nd CM590 casing. Will use the CM140mm fans as exhaust, along with CM's UV reactive 120mm fan (the casing will have extensive UV lighting scheme), and a 120mm Panaflo (more CFM than this CM "90CFM" fan, based on unscientific personal "hand feeling" test), plus CM's 120mm silent fans for the rest.

On their own, I would say they are relatively quiet. It's just that once you have many of them together, plus 2 other rigs in the same room with multiple fans each, every little bit of sound adds up and the result can be loud.

I've been testing (non-scientifically, just using my hand and my own estimate of which fan has more airflow) a few 120mm (CM "90cfm", Panaflo 103cfm, Silverstone (forgot model #, it came with NT06-Lite heatsink), CM silent fan, CM blue LED (several models), Vizo "UV" LED, CM UV reactive fan), fans for my recent rig builds, and came to the following conclusion:

1. CM "90cfm" fan > Enermax Twister Magma (IIRC rated at 69cfm, correct me if I'm wrong pls).
2. Panaflo 103cfm fan is much more powerful than CM "90cfm" - difference felt a lot more than difference in #1 (so official cfm diff of 13cfm between Panaflo and CM felt more than the official difference of 21cfm between CM and Enermax)
3. CM "90cfm" fan > Xigmatek XLF (the one with white LEDs)
4. CM "90cfm" fan > 140mm CM silent fan (rated at 60cfm)
5. CM "90cfm" fan LEDs still working after >1 month running 24/7 - wondering when it will start to die since I have an older rig with CM LED fans and most of the LEDs already dead (but those fans about 2 years old)

So I concluded using my completely unscientific and inaccurate method that CM "90cfm" is probably (if Xigmatek, Enermax and Panaflo uses accurate cfm numbers) around 75-80cfm. For RM28-30/fan, it's pretty good and powerful, just that you will worry the LEDs won't last.

I currently have 8 of them running in 3 different rigs. One rig (CM590) has 5 of them (3 exhausting - top 2x, rear 1x; and 2 intakes - side window, HD cage) and it has allowed me to have CPU (E6600 overclocked, Zalman 9700) full load temp at 45-47C in ambient 30-33C, and GPU (9800GT, Zalman VF900-Cu) full load temp at 51C.

On a side note: of all the fans I tested, the Silverstone was the most powerful (it was a thick one = 38mm width), I forgot the model number, but it was bundled with their NT-06Lite heatsink. Definitely a "finger-chopper" fan if you're not careful. Kinda noisy at full power too.