Comment 87 for bug 408165

emory: known issue with the driver, unfortunately. The easiest workaround is:

1. Disable networking in Network Manager applet (right click -> uncheck Enable Networking)
2. sudo ifconfig ra0 down
3. sudo modprobe -r rt3572sta
4. sudo modprobe rt3572sta
5. sudo ifconfig ra0 up
6. restore networking in Network Manager

Basically, yanking the driver out of the kernel and re-loading it fixes whatever broken state the driver works itself into over time. Obviously this is not suitable for production use, e.g. in a dedicated 24/7 computer in an internet cafe or a dedicated server. I wouldn't count on Ralink fixing it any time soon, either. Our hopes are on the mainline kernel ralink drivers to eventually pick up support for this chipset, but last I checked, it doesn't.