Sign up for the keys:
Get the finger print of your key.

Example:

Edison@CYBERCR /c/Java/jdk1.6.0_26/bin

$ keytool -list -alias androiddebugkey -keystore ~/.android/debug.keystore -storepass android -keypass android androiddebugkey

Certificate fingerprint (MD5): E2:57:DD:DE:99:AD:B3:E9:AA:D9:FB:CD:31:39:47:5A
Get the key from Google.
Demo Source Code.
Another good tutorial.