In fairness, the article you linked says nothing specifically about PSA levels. It mentions symptoms of BPH being reduced, but not PSA levels one way or the other.
But, when I did google "CIALIS PSA LEVELS" I found this: Which Medicines Affect PSA Levels? | eHow
Specifically states that viagra and cialis don't affect PSA levels one way or the other. There wasn't much information out there, but I could find nothing at all that supported the statement that Cialis lowers PSA. I found many mentions of its effects on BPH, but that was it.
Did you mean to say that Cialis affects BPH instead of saying it will "drop your PSA like a rock" or is there simply a study that I can't find with my searches?
I have used Cialis for a long time primarily for its health benefits. It does help with BPH by relaxing the muscles around the prostate and by dilating the blood vessels throughout the body. This is also how it helps to lower BP. Its good stuff.