Sony Music delivered a knockout blow to CDs, announcing recently that on May 1, it will cease sending promo CDs to critics and journalists, and instead only provide them with digital previews. Sony is the second-largest music company in the world, and the first major label to do digital-only promotions–hopefully it’s not the last.

This is only a toe-in-the-water attempt at ending all CD production for good, but it’s still a good indicator of where the industry is eventually heading.

Over the last decade, overall CD sales have plummeted 48% in the U.S., declining steadily almost every year. Meanwhile, digital sales continue to rise, growing 27% in 2008 and 8.3% in 2009. Digital downloads now represent 40% of all music purchases. What’s wrong with major labels, right? The business model seems obvious: Go digital.

Unfortunately, CDs are far from finished. Why? Because digital revenue has failed to compensate for declining CD sales, and more importantly, compact-discs still account for 80% of all album purchases–the labels’ bread and butter.

So it’ll likely be a while before we’re 100% digital, but Sony’s move will definitely encourage other labels to follow suit with promos.