Syria presents a great example of how controversies can be fought on Twitter. Although these are not solutions based on proving your ideas, they are more like denial of service attacks.
What is happening is that the protesters in Syria are using Twitter to communicate. They created a hashtag #Syriaprotest to send out notices about where they are going to demonstrate and other logistical coordination. The Syrian government wants to interfere with the protests, so what they are doing is spamming the hashtag. They have an automated system that sends thousands of messages containing pro-government propaganda to #Syriaprotest. No one believes the propaganda, but it makes it impossible to find the relevant tweets.
So the protesters have to create a new hashtag, communicate it to each other as secretly as possible, and then they have a few hours before the Syrian government figures it out and starts spamming that one too. Unfortunately, by the time a critical mass of protesters has learned the new hashtag, so has the government. And the cycle starts again.