Here's a neat little gadget/bot combo that could prove very useful for public waves if the system caught on.
Add the Karma Gadget and Bot to your waves and use it to rate your users (out of five stars). If users get consistently low scores, they will be automatically kicked from Waves that choose to turn on this option.
Of course there are some potential problems with such a tool: if a user expresses unpopular views in one wave and gets poor ratings, they might find themselves banned from any future wave that uses the tool, regardless of the subject. If the tool took off in popularity it could be quite horrible to find yourself on the end of such banishment.
On the other hand, if the tool doesn't get popular it would be unreliable for crowdsourcing opinions, letting in known trolls who had just not been rated on enough waves.
Despite these shortcomings however, I would love to see this developed further (and even be integrated as part of the official spam-fighting tools of Wave), as I see great potential in harnessing the opinions of others in keeping waves free from known trolls and spammers.
One potential use case is the immediate banishment of those frustrating bots that pop up all over the place (Kanye-bot anyone?). I'm uncertain whether bots are in the firing line (Karma-Bot itself seems immune and doesn't show up in the rating gadget). I'm also unclear about what happens if something like the public group (which can be rated) gets consistently bad reviews.
As of writing, the gadget does not carry out bans and won't until Google implement the kick-out feature. I will be following this tool as it develops, and I'll be looking for opportunities to use it. And if you see me on a wave that uses Karma, please be nice!