I was showing off SteroTube to a reader last week and he pointed out that we have never featured the app. I decided to remediate that immediately by mentioning that StereoTube is the best way to mix YouTube and MP3s on your PlayBook. It lets you create playlists with unlimited songs combining your YouTube and local MP3s together. The app keeps on getting improved and is under constant development with v3.0 coming out late last week.
Check out StereoTube for $2.99 in App World. Its well worth the price if you use YouTube as your streaming music provider like me.