I get the hits on my subscription CD twice a month and so I hold the three song rule. If three songs hit the charts and play daily on rotation I generally will purchase the whole disc. Thats been my rule for yrs. These days it rarely allows the need to purchase a full CD. Most of the CDs I buy asides the rule are personal choices like the Metallica CD. Bullet For My Valentine, Trivium and of course Barry does the 80's.