I have almost 5000 miles on my 99 GTS. I was down approx 3/4 of a quart at 500 miles when I changed the oil for the first time. I changed oil again at 3200 miles and was down about a quart. I run the car relatively hard during mostly in town driving and one track day. It's a bit hard to get consistent readings because of the 2 quart range on the dipstick, but I figure I'm using a quart every 2000 to 2500 miles or so.
Jim