It is difficult to gauge how effective the steroid policy has been. The media controls much of what the public knows about the game, and therefore controls their knowledge of steroid use. One thing it is hard to deny is the number of big names it has turned up in the past few years. Top players like Alex Rodriguez, Manny Ramirez, and Roger Clemens have all come under fire for their consumption of banned substances. They have all paid the price whether it was from suspension or public scrutiny.
Another important concept is that the results of this policy must be judged over the span of ten years or more. Use of performance enhancing drugs has become so widespread in Major League Baseball that it is difficult to determine which substances are being used from year-to-year. Until there is solid evidence that a type of drug has been completely filtered out, the statistics may not be relevant for another decade or so.
To give the commissioner some credit, he has the public on his side. He is working hard, or appears to be, on making the game better for years to come. Bud Selig has shed light on the problem and made it known that abusing steroids will no longer be tolerated.
At this point I would grade the policy: B. It has turned up many liars, the game is slowly becoming what made it a national pastime, and players who cheat are getting the suspensions they deserve. Let's check back in a few years.