MacBook Air 2010 OS X 10.6.8 w/Broadcom wifi disconnecting: "Disassociated because station leaving"
I have the same problem and I've also been looking around a lot. The only thing I find is that if you have an Atheros Wi-Fi hardware in your Mac (I just found out that I did, mid-2011-iMac) this will help:

http://rys.pixeltards.com/2011/09/04/osx-lion-wifi.html