Each address has an interface identifier that is derived from the MAC address, which is globally unique. There is built in duplicate address detection. It works much like the IPv4 autoconfiguration with a much lower probability of collision - probably none. If the interfaces sees multiple RAs then it means the host can have multiple addresses. Tom noted that IPv6 uses dynamic DNS to update the DNS when an interface's address changes.
Router advertisements contain a default router list.
Each host picks this up and maintains a local list of default routers. The host keeps track of reachability to all neighbors, if necessary the host can send probes. Inc. Stuart began describing the current status of getting PacBell ADSL at up to T-1 data rates. Stuart infers that IPv4 addresses are becoming scarce. People are finding an arbitrage around additional cost per address in the deployment of NATs.