Using Fedora 16's kernel 3.3.0-4.fc16 I'm intermittently seeing freezing during poweroff/reboot process. SysRq key works and killing all existing processes continues the poweroff process (see traces in related Fedora bug). The bug had been appearing for me in Fedora's builds of 3.1 and now again in 3.3. Currently running on 3.2.10-3.fc16; none of the 3.2 builds seem to have this problem. Apologies if this is the wrong place for this bug, but nobody is responding from Fedora/Redhat...
It should go to Fedora. If sysrq/kill works its almost certainly a user space bug.