Personally, I agree with those that say Apple should stick to their own HIG and only put metal on hub apps. I actually don't mind the metal finder at all, but conceptually it and Safari should both be Aqua.
My personal main reason for preferring Aqua on things like that is not the color scheme, but the flexibility of a standard aqua toolbar--drag and drop items from a pane to make it exactly what you want. That's one of the reasons (despite being able to turn things on and off in Safari) I prefer Camino to Safari, and I love being able to build my own toolbar in Mail. The customizable bar was one of the best interface ideas Apple's had in a long time.
All that said, here's a different perspective on metal. Think back a few years to OS8/9. What color was the OS? Grey, with a click-and-draggable border around windows.
Then came white and pinstriped Aqua with no window borders (but a drop shadow to provide some definition), and there was a great hew and cry from those who wanted the grey.
The new Panther metal look is much flatter and smoother than the old one (more like matte-finish aluminum than brushed metal), so it's basically slightly shiny-looking grey with a click-and-draggable border around windows. Not really so different from OS9.
We've actually, in a way, come full circle. For me, the ability to drag a window by it's edge is the biggest unsung advantage of metal over Aqua, and one of the reasons I'm secretly glad that the Finder uses it now (coupled with the smoother look).
Just giving folks a bit more choice would be a nice concession on Apple's part--maybe an aqua-styled, metal-like interface.
