The new nVidia forum is already up to its eyeballs with spammers.
Checking in with phpBB shows they are more experienced than most at combating the spambots.
The old CAPTCHA was defeated rather quickly. This has been replaced by a question and answer but again the spammers have been able to get past that.
The latest idea to stop the spambots is a new approach that requires a new registrant to sort things into one of two columns. So far this has held the spammers at bay. There are lots of things that can be sorted so automated attacks will not work easily.
Spammers do not gain any advantages as the robots.txt file keeps search engines out. So the spam links are useless.