Update 8/4/05: Using the hack described below will prevent your menubar status items from loading properly if you're using ShapeShifter 2.1.2. This will be fixed in a future version of ShapeaShifter. In the meantime, you can work-around the issue by entering the following Terminal command:
defaults write com.apple.systemuiserver NSGrayBackground -bool false

Remove the work-around with:
defaults delete com.apple.systemuiserver NSGrayBackground

---

So I just happened across something I found interesting in Mac OS X. Turns out there's a built-in way to make any Cocoa application use an all-metal window appearance.

To globally set all of your Cocoa apps to use metal, do this in Terminal:
defaults write NSGlobalDomain NSGrayBackground -bool true

To set a particular app, find its bundle identifier (found in the app's Info.plist file) and replace NSGlobalDomain with the bundle identifier. Or, use Property List Editor to set that NSGrayBackground boolean key to true for the app's preferences file.

To go back to normal, do this from terminal:
defaults delete NSGlobalDomain NSGrayBackground

Tested on Tiger with Mail.app, System Prefs, and TextEdit. Use at your own risk.