One of the primary reasons that I do not use provider STB's -- the inability to transfer content off the device (that and the monthly rental fees). Pretty much every provider has this restriction.
I personally use TiVO for my STB as there are a variety of tools for allowing the transfer of content. I happen to use a PLEX server to store content I have yet to watch when I approach the storage capacity of my TiVO. The only content you can't transfer is that which is marked as copy protected by the originator (HBO, for instance, commonly does this).