Wireless sensor networks have been traditionally designed to be privately owned and used. Hence the two hallmark features of sensor networks, namely customized network applications and the collaborative in-network processing, are not achievable beyond the boundary of the users' administrative domains (except for limited scope data sharing through Internet gateways). This position paper advocates a contrarian notion of sensor grid that preserves the operational continuity of the participating sensornets and yet allows controlled sharing of sensor node hardware capabilities over multiple administrative domains. This is achieved by stitching together virtualized nodes donated by participating sensornets into a transient virtual sensornet underlay, which is called a Community Sensor Grid. Possible approaches for node virtualization support are discussed for some existing sensornet OS platforms. The formation, operation and dissolution of the transient underlay are to be supported by a P2P overlay formed by the Internet gateways of participating sensornets.