JKR's website

[nrenka]

No: HPFGUIDX 128847

...has been updated.

Of much interest is an answer to the "Why didn't the Ministry use 
Veritaserum?" question, at 
http://www.jkrowling.com/textonly/faq_view.cfm?id=105

"Veritaserum works best upon the unsuspecting, the vulnerable and 
those insufficiently skilled (in one way or another) to protect 
themselves against it. Barty Crouch had been attacked before the 
potion was given to him and was still very groggy, otherwise he could 
have employed a range of measures against the Potion - he might have 
sealed his own throat and faked a declaration of innocence, 
transformed the Potion into something else before it touched his 
lips, or employed Occlumency against its effects. In other words, 
just like every other kind of magic within the books, Veritaserum is 
not infallible. As some wizards can prevent themselves being 
affected, and others cannot, it is an unfair and unreliable tool to 
use at a trial.

Sirius might have volunteered to take the potion had he been given 
the chance, but he was never offered it. Mr. Crouch senior, power mad 
and increasingly unjust in the way he was treating suspects, threw 
him into Azkaban on the (admittedly rather convincing) testimony of 
many eyewitnesses. The sad fact is that even if Sirius had told the 
truth under the influence of the Potion, Mr. Crouch could still have 
insisted that he was using trickery to render himself immune to it."

Veritaserum can be resisted.  It is not considered infallible, but 
can be argued against in such a way that the testimony from it can 
always be quibbled with.  Crouch was never going to let Sirius have 
that chance, either.  One can use Occlumency against Veritaserum--
oooh, nifty.  Discuss!

-Nora gets back to finishing the #2 out of 3...