Unfortunately, attacks against CAPTCHAs aren't limited to sw bots:
http://www.technologyreview.com/blog/mimssbits/25594/

<snip from above>

"How Spammers Use Low-cost Labor to Solve CAPTCHAS
Workers in Russia, Southeast Asia, and China are paid a pittance to solve millions of CAPTCHAS.

CHRISTOPHER MIMS 08/11/2010"
</snip>

ymmv,

C.G.

On Wed, Dec 15, 2010 at 3:27 PM, Lisa Kachold <lisakachold@obnosis.com> wrote:
>
> On most of my production Drupal sites, I CANNOT even enable comments.  It's a sad day when one cannot have a login based access that is not hit by SPAM bots?
>
<snip>