You can use the app to search for videos by keyword so that you won't have any trouble finding what you're looking for. Once you have what you need, you can simply add it to any of your playlists.
As you would hope, PlayTube Free works perfectly by running in the background. That means that you can listen to the songs on your playlists while using your Android for any other purpose.
PlayTube Free is a good tool that you can use to turn YouTube into your personal radio station. Just make a few different playlists with your favorite music, and choose the one that fits your current mood.
Requires Android 2.1 or higher.