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:
It would appear that baseball was much quicker in stopping use of the drug than many other sports, such as track, football and soccer, have been. While it is possible that later, as-yet-unknown substances are yielding negative results for players who are actually using steroids, the lack of finding of THG and DMT (another designer steroid that was withheld from public knowledge), gives a solid indication that their use is limited.
Even before restructuring the whole thing to make it tougher in January, baseball's steroid policy appears to have been working.