I'm running a 32bit userspace on an amd64 kernel. Everything works fine in general, except that I cannot get WPA to work on my rt73usb card.
iwconfig and "iwlist scan" returns correct and meaningful results,
but wpa-supplicant gets confused. When I ask it what access-points it's seeing it gives me a list that seems to have the right number of elements, but they're all marked as WEP (rather than a mix of WEP, WPA, and open),
and their mac address all look like "0000010000NM" where "NM" seems to be the first 2 hexa chars of the real mac address of the access point.
All in all, it looks like some part of the kernel (presumably somewhere in the wifi code since everything else works correctly) handles 32bit syscalls in 64bit kernels incorrectly.
I've tested it with a 2.6.24 kernel and the included rt73usb module. When using the 686 build, the wifi connection works dandy (but I don't get to use all my RAM ;-(.
This is a wpa_supplicant/ioctl bug, I think you should report it to the wpa_supplicant maintainer..