An application when installed on a device or on an emulator will install at:
/data/data/APP_PACKAGE_NAME
The APK itself is placed in the /data/app/
folder.
These paths, however, are in the System Partition and to access them, you will need to have root. This is for a device. On the emulator, you can see it in your logcat (DDMS) in the File Explorer tab
By the way, it only shows the package name that is defined in your Manifest.XML
under the package="APP_PACKAGE_NAME"
attribute. Any other packages you may have created in your project in Eclipse do not show up here.