Great post, I'm working on my build tonight and this'll come in handy. I usually end up just changing the Maps API key locally and never committing it which kinda sucks.
For Eclipse you can set the debug key here: Window > Preferences > Android > Build > Custom debug keystore. That's for the normal Eclipse/android build process.
Comes in handy when developing on multiple machines as you can't update an app that was signed with a different debug key (must uninstall first).
I was also using a debug/release flag previously but kept forgetting to change it when I sent the release build out for testing.