Here's my take on the Camaro/Mustang/Challenger thing...
Challenger: A bit "too retro" for me, but they got it pretty close to "right" for what a new Challenger should be. The Challenger only ever had one basic style, so building off that one style was the only way they could go with it, other than just putting the challenger name on something totally new and nothing like the original, like they did with the Charger. I haven't seen the sales figures on the Charger, but there seems of complaints about the number of doors from the enthusiasts... something tells me the people buying these aren't enthusiasts though. The Challenger was a pretty short-production run then, and I'll bet if it comes back, it will also be intended to be a 3-4 year run, with no intention of making a return after that. (just my take on it, correct me if I'm wrong) They didn't leave much to be changed without upsetting the look of the original style they based this one from, so I doubt this car will go through any major styling changes before the model is dropped.
Camaro: first-gen enthusiasts want "more retro", but they seem to forget that the first-gen was only 3 years of the 35 years the camaro was in production. There was some pretty cool styling in those other 32 years too. It appears GM might want to bring the Camaro name back for another 35 years, which is why they designed it to allow for styling changes to stay fresh. If they made it look like a '69, the first time they'd change something, it would just look like something that didn't fit the '69 styling. The design, as-is, can be changed dramatically without redesigning the whole car through a 7-8 year production run. The next style could build off this one, or go completely different, without something looking out-of-place in the evolution of the Camaro. It might not sell as well for the couple years a full retro would, but this appears to be a long-term design, not a "Jump on the retro fad while it lasts, then kill it again" design.
I know a lot of you have said something like "I'd buy one if it was a fully-retro '69 style", but they don't want you to buy one. They want you to buy several... one every few years when the new design makes you want a new one more than the one you already have.
Mustang: Where does it go next? 2010 Mustang II?
They got this design out way before the others, and it was a hit. The problem is, much like the Challenger, there's very little room for change without upsetting the whole retro look. People won't buy retro forever, but the one thing the mustang has going for it, is the hype of the retro Challenger and semi-retro Camaro. This hype will buy the Mustang a couple more years of reaping the "retro" fad. My question is, what do they do when sales fall off? (and they will, you know they will)