My 99 SVT uses about 1/2 to 3/4 of a quart between changes, which I do every 5,000km (3,000miles).
I have about 44,000km (27,000 miles) on it now, and it's used oil at that rate since I bought it with just over a 1,000 miles on it, so I'm not too concerned.
As a general rule of thumb, I've always heard from mechanics I've known over the past 30 years that anything up to one quart per 1,000 miles is acceptable, assuming the engine consumes oil at that rate consistently. If oil consumption is at a quart/1000 and rising, you likely have a problem.
