In the midst of all the talk of today's hearings, a Will Carroll article (pay site) sheds some light on the facts:
In 2003, 96 players tested positive for steroids.
In 2004, 12 players tested positive for steroids.
There were no positive tests in either year for THG, the drug most commonly associated with the whole BALCO deal. To quote Carroll:
Even before restructuring the whole thing to make it tougher in January, baseball's steroid policy appears to have been working.