Create a page that highlights applications that are making use of data from data.gov. The examples should be real world (not demo's) sites that currently are making use of the data. They should range from simple to more complex. The public should be able to submit their sites to list. Possibly to encourage the use of the data prizes should be given out for the "best" sites, chosen by the goverment, or by public voting.
Contests to make use of the data would give insentives for the data to be used, and possibly create more value, and show the value of the system (it may also encourage larger buy-in from the different branches of government) and encourage local goverments to provide more data.