NetworkManager-0.9.2-1.fc16.i686 works fine. Upgrading to NetworkManager-0.9.4-3.git20120403.fc16.i686 or other 0.9.4 doesn't. Wireless networks are shown, but they are grey and can't be enabled. Up- and downgrading indicates that the problem might be in nm-applet. Just downgrading to 0.9.2 and restarting the service is not enough. Only when the applet is restarted it works. (The applet sometimes segfaults when it is running while up/downgrading. 0.9.2 due to ERROR:nm-utils.c:1228:nm_utils_security_valid: assertion failed: (have_ap)) This is on a live image with bad logging. Dell Latitude D510. Let me know what debug information is needed ... if any.
Looks like https://bugs.archlinux.org/task/29597
*** This bug has been marked as a duplicate of bug 815331 ***
Yes, I was using fallback mode - I had not considered that that could make a difference. That also explains why I haven't seen the issue before. I will do some testing on monday.