I haven't been on the site in a while and I am amazed at what is/has come out of this community in the past 8 months.
Anyway, I made a blimp last year for a class at RISD taught by Paul Badger. The blimp follows people. Its based around the arduino, a pyroelectric sensor, and an ultrasound sensor. The code is quite simple: it scans for heat (IR at ~ human frequency) and once it finds a maximum above threshold, it moves towards the location of heat and corrects for height.
I started out with some mathematically complex programming but soon learned that very simple rules performed satisfactory. I don't plan on adding any more advanced controls or processes: its simple, stupid, and fun.
A video of the blimp is here
also on the video is some other stuff I've done including a drawbot that draws in polar coordinates, and a bicycle powered record player (hah, not done).