If the Shelby were the original projected $38-40k, it wouldn't be too bad. But the markup is ridiculous. I've heard similar stories to the one posted above. One guy I talked with had a coworker who preordered a Shelby--even putting down a deposit--and when the guy's Shelby came in, the dealership sold it out from under him to a person who was willing to pay more (the person ordering the Shelby was supposed to get it for MSRP.)
As was mentioned above, I think the greatest strength of the Shelby will be its value years down the road. Other than that, if you are just looking for a performance car, either a supercharged/turbo GTO or a stock Z06 (since Shelbys are being marked up into Z06 range) would probably do ya better.
One thing I haven't heard about, but I suspect that the Shelbys will take a hit on insurance. From what I've seen in the past, limited production special versions of cars take a good sized hit over the regular version.
Speaking of Mustang Markup, I remember seeing a new 05 6 cylinder Stang (non-convertible) that a dealership was asking $34k for. More than a GTO for a nonconvertible 6-banger. :willy: