I'm a Believer
Purchased one of these a year ago.  I am a college student living in a one bedroom apartment in the midwest and I seem to always get the flu once a year, and a cold at least once (usually more) per year.  Since purchasing this, I have not gotten either.  The past year was a bad one for the flu, and there was a lot of colds going around, but I never got it one time!  It is not silent, but the noise is pretty minimal, I would compare it to the fan on a computer.  My apartment is about 750 sq feet so it is probably a little too big for just one of these, but I still believe that this little gadget kept me flu-free for a year, so that is $40 well spent!
Rating: 5 stars