In current Rawhide (selinux-policy 3.10.0-71.fc17), virt-manager fails to connect to libvirt on startup. /var/log/messages shows several SELinux denials:

Jan  4 18:06:50 adam kernel: [16006.077329] type=1400 audit(1325729210.793:658): avc:  denied  { read } for  pid=888 comm="polkitd" name="2" dev=tmpfs ino=23046 scontext=system_u:system_r:policykit_t:s0-s0:c0.c1023 tcontext=system_u:object_r:systemd_logind_sessions_t:s0 tclass=file
Jan  4 18:06:50 adam kernel: [16006.077344] type=1400 audit(1325729210.793:659): avc:  denied  { open } for  pid=888 comm="polkitd" name="2" dev=tmpfs ino=23046 scontext=system_u:system_r:policykit_t:s0-s0:c0.c1023 tcontext=system_u:object_r:systemd_logind_sessions_t:s0 tclass=file
Jan  4 18:06:50 adam kernel: [16006.077360] type=1400 audit(1325729210.793:660): avc:  denied  { getattr } for  pid=888 comm="polkitd" path="/run/systemd/sessions/2" dev=tmpfs ino=23046 scontext=system_u:system_r:policykit_t:s0-s0:c0.c1023 tcontext=system_u:object_r:systemd_logind_sessions_t:s0 tclass=file
Jan  4 18:06:50 adam libvirtd[4487]: 2012-01-05 02:06:50.795+0000: 4489: error : remoteDispatchAuthPolkit:2459 : Policy kit denied action org.libvirt.unix.manage from pid 4747, uid 1001: exit status 2
Jan  4 18:06:50 adam libvirtd[4487]: 2012-01-05 02:06:50.795+0000: 4489: error : remoteDispatchAuthPolkit:2478 : authentication failed: authentication failed
Jan  4 18:06:54 adam libvirtd[4487]: 2012-01-05 02:06:54.047+0000: 4487: error : virNetSocketReadWire:996 : End of file while reading data: Input/output error