Industry and academia demonstrate connection handoff across wireless LAN, GPRS, wired LAN on commercial networks: A press release (not included on this site) says that TeliaSonera, Ericsson, Radionet, and the Helsinki University of Technology have demonstrated a seamless handoff across commercial networks. The benefits they cite are absolutely the case: users want uninterrupted services and no monkeying around.
Interestingly, if you use NetMotion Wireless software, you can achieve most of this effect today. While you're responsible as a user for changing your connectivity, the NetMotion client and server software maintain the persistent state of the Internet connection.