This one has taken me quite a while to find out, with bits of information here and there. Two steps only:
Blacklist rt2800usb in your /etc/modprobe.d/blacklist.conf, preferably with an explanatory comment to yourself why, or at least something like #My own blacklist starts here
Then at least one place recommends to add this line to the end of your /etc/rc.d/rc.local file
iwconfig wlan0 power off
I'm not really sure the second is required but had done it before blacklisting the module, and it works. Check for yourself if it works for you without the second entry.
That's it. Glad I finally finished a complete system upgrade without reinstalling. It's all 13.1 now and sound, video acceleration, wireless all work.