Silent systems are usually reserved for special-case offices, like hospitals, sound laboraties, and some offices where concentration is key.
I've come in contact with two of these things...They're okay, but they're bytch heavy, bytch expensive, bytches to install and use, and they're not totally cool. If you put a lot of really high-end stuff in there, it's gonna get warm. Not to mention that, despite having no fans, these things do actually fill up with dust amazingly fast. It's like magic.