According to http://www.businessweek.com/articles/20 ... ruck-trend the White Castle Cravemobiles will be headquartered in Louisville and Columbus starting this month. They will be used to test locations (e.g.: if lots of business at a particular location, they may put a brick/mortar building there) and menu items, as well as providing more standard sliders.
Also using food trucks as mobile test market platforms (but not yet scheduled for Louisville) are Wendy's, Taco Bell, Appleby's, Sizzler, and Chick-fil-a.
It's interesting that White Castle expects an 18 month payback for the food truck investment!