As you know the FAA is midway in a long rulemaking process to figure out how to integrate UAVs in the national airspace, but the bottom line from the inititial recommendations are as follows:
For us (non-commerical hobbyists), you must stay within these limitations:
--fly within line of sight
--under 400' alt
--under 30 knots
--Fly at least 3 miles from any airport
As you're designing your airframes, keep these limits in mind!