With thunar-volman-0.8.0 a USB device is added to the side pane. Right clicking and choosing unmount hangs with Thunar maxing out CPU until process is killed. The volume is unmounted successfully but Thunar remains hanging. Slackware 14.1 Xfce-4.10 thunar-1.6.3 udisks2-2.1.0 gvfs-1.16.3
I can't reproduce this in 1.6.4 on Slackware -current (post 14.1 devel), for what it's worth; I don't have a 14.1 system that I can easily test, but I'll try spin one up and see what happens.
Okay, now that I'm home, I'm able to test this on a few different 14.1 systems - still unable to reproduce. If you can get more information about the hang (perhaps open thunar in a terminal window and see what shows up there when it hangs), then post it here. It's also worth noting that thunar will hang if there's any mountpoint on the system that's inaccessible (e.g. a stale NFS mount), so be sure that's not the culprit... Marking this WORKSFORME, but feel free to reopen if needed.