In software development there are tons of various challenges or competitions, just take a look at stackoverflow.
Also, there are challenges with huge prizes involved, such as for netflix competition (data mining task for movie recommendations).
Even more, in software development learning is usually by solving puzzles, varying from such simple tasks as reordering of a stack or reinventing dijkstra algorithm to more complicated, such as AI for checkers.
These puzzles/competitions are not only great for competing, but they also 'force' you to search, study and improve your skills.
After having a quickie with google, I couldn't find much. There was a poster competition, we can also say that TSP or VRP is somewhat of GIS challenges. It seems that ESRI also held some kind of competition.
So my question is as following -- are there any competitions or (even more importantly) puzzles (for learning mostly) for GIS?