Art,
Here are some weights. Size 12 or 13 depending on the brand. Note that the XC Flats do not have rock plates. Weights are for each shoe, not the pair. These were weighed on my scale, not manufacturers' weights. I included the Salomon XA Pro as a comparison, as it is one of the most popular running shoes. One of the problems with XC flats are no rock plate, not real grippy soles, and they wear out quickly. I am doing a lot of hiking now with my Perigrines, as they really grip surfaces well. My favorite for comfort (other than impact and cactus) is easily the Mizunos. The other 3 XC flats did not last even 200 miles, but keep in mind they were on a lot of cross country hikes and nasty volcanic rock.
XC FLATS
Mizuno Wave Universe 4 shoes = 4.9 oz
Asics Piranha SP 2 Racing flats = 5.3 oz
Saucony Kinney XC Flasts = 6.5 oz
Saucony Shay XC Flats = 7.2 oz
RUNNING SHOES
Saucony Perigrine = 11.5 oz
Salomon XA Pro 3D Ultra Trail Running Shoes = 14.70 oz
OTHER
Vibram Five Fingers KSO = 6.7 oz