With little doubt, the fastest growing and most influential Web 2.0 technology has been that of the Social Networking site. Sure, the concepts have been around for quite some time - harking back to the first dial-up BBS' of the 1980's - but the growth of sites like Facebook and MySpace is unheralded. The amount of time people now spend "Social Networking" has even overtaken the quest for porn (see the BBC's "Porn putting on its Sunday best").
Now, if you combine the facilities of social networking sites to coordinate large groups of people incensed by another group with tools that enable members to "donate some of their computers bandwidth", you can quickly develop massive "opt-in" DDoS systems.
The first component - the groups of incensed and motivated members - are already out there. Just look at the Facebook groups that sprung up backing either Israel or Hamas in the most recent conflict, or older groups such as the animal cruelty activists like "Stop Huntingdon Life Sciences Animal Cruelty".
The future of Social Network initiated/coordinated DDoS attacks is just around the corner (if it hasn't already happened in less-than-newsworthy cases already). Welcome to the birth of SDoS - Social network Denial of Service.
I posted a longer blog on the topic, along with the tools available to activist and social conscience groups - and some future threat motivations up on the IBM Frequency-X Web site.
Take a gander at "Social Network Denial of Service (SDoS)?" for more thoughts and analysis.