Providing intelligence to the manufactured objects to be self-aware, to respond to the changes in it's environment is the essence of the Wireless Sensor Networks. How nice it will be if your Computer network can also control your office lighting, airconditioning requirements and your phone systems. This is possible only if these disconnected networks talk to each other. WSNs has the capability to make this happen.
WSNs combined with RFIDs increase the range of RFIDs, thus reducing(not eliminating) the needs for costly RFID readers. This can be done by using a network of sensors to pickup the signal from RFID tags and relay that signal thru the network to the nearest RFID reader.
I can provide an excellent example of connecting your complete house with WSNs, but then I may invite the wrath of privacy groups, instead tomorrow I will present an example of RFID and WSN usage in industrial environment.