I worked on some robotics research not too long ago. We used an arduino for interacting with motors, sensors etc. We ran some semi-interesting filtering on the data before passing it back to a more powerful processor that ran a python program that did the decision making and provided interactivity from the user.
The main reason we used the arduino was compared to all the alternatives (other similar hacker boards, and FPGAS say) it gave us a flexible toolkit, easy deployments to a board, and a very simple way of interacting directly with sensors throuhg a fairly convenient API.
The main reason we used the arduino was compared to all the alternatives (other similar hacker boards, and FPGAS say) it gave us a flexible toolkit, easy deployments to a board, and a very simple way of interacting directly with sensors throuhg a fairly convenient API.