A number of proposals (not all serious) have been floating around lately to redraw the borders of the US. According to this list nearly every US state has groups wanting to partition it somehow. One idea was fifty states with equal population. Another is to redraw borders based on the actual communities that exist--in this case measured by how dollar bills travel:
Dirk Brockmann, a physicist, used information about dollar bill travel patterns from WheresGeorge.com to track the movement of currency. He then used that information to re-allocate the US into states based on "effective communities." Specifically, he drew borders where dollar bills are least likely to cross.
There are a few interesting borders that jump out. Both Pennsylvania and Missouri are divided into eastern and western chunks. Major metropolitan areas that currently cross several state borders (eg Chicago) have their own state in Brockmann's map. Notice also that the northernmost part of California is lumped together with Oregon and Washington--not unlike the proposed State of Jefferson. Dollar bills do not appear to cross the Red River from Texas to Oklahoma very often.
One component that would be interesting to add to this is how dollar bills travel internationally. US currency is frequently used in other (especially developing) countries so it would be neat to see how a dollar bill moves around once it's outside of the US. Does it stay in the first non-US country it reaches, or move around more from there? This data could also be incorporated into a project like Brockmann's: some communities near international borders might trade with neighboring countries more than they do other parts of their own.