The attacks Arduino.cc's has been suffering, are Bot attacks, and bots "cannot" navigate sites protected by "good" implementations of CAPTCHAs, such as the format used over at Yahoo.
It's trivial to break any captcha. You simply link it into a "free porn" site and have users answer the captchas. They type the captcha, the bot automatically enters it into the victim site, and if it's right, the script lets the viewer have their porn. There is no such thing as a good implementation because any captcha can be defeated with this sort of attack.
I haven't heard of that one before, how does it work?
If CAPTCHAs are so easy to defeat, then the brains over at Carnegie Mellon University have a lot to be held accountable for, and gosh, the cheek of it, they're still telling people to use it!
Our portfolio includes a number of adult sites we've owned "for years", all with CAPTCHA, not one has ever suffered a spam attack. An adult forum we own started out with Yabb, but it got too big and we upgraded it to SMF. In its 3 year history only a handful of Russians have tried manual attacks, but the site has 3 moderators and they blocked the IP's before they had a chance to do anything.
Spam is completely preventable.