A challenge
One way to use these sensors is to use two sensors to actually "find" an object. This can help your robot actually find the position of specific obstacles. How this is accomplished is detailed on the maxbotix.com website at: http://www.maxbotix.com/documents/MaxBotix_Ultrasonic_Sensors_Find_Direction_and_Distance.pdf. You have all the knowledge you need to add this type of capability to your robot.