In March of 2003 Circuit Cellar published a feature article on using position sensing detectors (PSD). The project builds a 2D position sensor using a PIC16F873 as the microcontroller, an Aculux PCB set and a Hamamatsu PSD. Since that project is now over 10 years old, what modern project or device configuration can I use to get the same or better functionality?
That is still a good approach. If the terrain is even, like a hard floor, a laser mouse sensor is a good option.
On the extremely complicated end, computation and algorithms have come a long way, so things like LIDAR or Microsoft Kinect for room navigation is much more feasible. But for low-end sensing, I don't think there is much difference now.