As a stop gap, your account has to be at least 24 hours old to post or comment. We will likely remove that after we get a better solution implemented.
On reddit, if you don't have enough Karma, you need to complete a reCaptcha to comment/post. Would something similar be possible here? I doubt people are willing to put much effort into spamming Hubski, so you probably wouldn't need a very hard human verification. I imagine messages like "What is 7 plus the amount of seconds in a minute?" would be easy to generate and easy to answer.
I'm fearful the continued use of the new rule will mean that people who have been lurking without an account will only be pressured to create one by wanting to get involved in discussion. If they then have to wait a day to actually get involved, new voices may miss a chance to 've heard on topics they actually care about. If I found a site where there was no real benefit to joining for a day, I'd be more likely to look elsewhere. Lurk more is a good principle, but I think it is one best encouraged through suggestions rather than set rules.