I'm having this problem since I installed Ubuntu 12.10 and it's driving me insane.
I have a NAS (DNS-320) that is running Samba. When I try to transfer a folder that has many other files inside it's very common that the transfer will just freeze at a certain point.
In the Unity interface the Nautilus icon will have that progress bar and the transfer window that shows file progress just freezes and can't be closed. The only way I can restart the transfer is by terminating the nautilus process with a -9 signal.