Yes, they can, in the words of Barack Obama’s election campaign. That campaign itself provided evidence that the tools of “Web 2.0″ – the community-driven web – can really make a difference, delegates at the Terra future conference in London heard this week.
From New Scientist comes a short article that explores whether social networks can engender social and political reform. The article has a number of interesting links to serious Web 2.0 and mobile applications designed and used for serious purposes. Are these exceptions or are they a harbinger of a slew of more applications designed to support democracy?

I think people would conclude that social networking and, in more general terms web 2.0, has already changed the world – just talk to anyone globally younger than 30 with internet access. These people already use the internet for the main purpose of listening to others and being able to then voice their own opinions.
I think saying that these applications are “designed to support democracy” though is misleading. The majority of the applications primarily are commercial in nature as they need to be in order to pay for the infrastructure that supports them – so they are therefore primarily designed to make money by fulfilling a need. The uses they are put to are diverse, but yes, perhaps the underlying consequence of fulfilling people’ needs is that they do support democracy by providing people with a voice.
As you quite rightly imply, that right to a voice is democratic – why else would repressive totalitarian societies seek to control what people are saying?