Looking at the source, it seems to be built with jquery isotope plugin. I couldn't see any similar examples at isotope site. Any one else know more details on the implementation?
Also, the job growth numbers for each city look suspicious. Was there such a jump in growth rate in Jan '11?
The animations are done with JQuery's .animate method, and since the stats are all across different ranges we're using D3's .scale and .quantize methods to normalize our positions.
If you have more specific JS questions than that I can point you at @golike who wrote all the code for this :)
Also, the job growth numbers for each city look suspicious. Was there such a jump in growth rate in Jan '11?