I've seen this mentioned by others but I think it's worth repeating.
Politics is undergoing (or has undergone, depending on how you measure such things) a fundamental shift in emphasis, from broad movement politics to single issue campaigns.
What has caused this splintering is an interesting question. You can see factors of it in a general disullusionment in politics and in particular politicians. Single issue campaigns don't ask you to sign up to a particular ideology, or believe in a particular person, etc. In short there's a lot less trust required. And I don't if you've noticed, but trust in politics and politicians has reduced recently.
The second major factor would be social networking sites. Facebook, and twitter particularly, but the other ones as well. The quick spreading of popular campaigns and the ease of joining them (one click and you're part of a group backing something) means being (however minimally) politically active is easier than it ever has been. That is not to say that many of these movements can actually achieve much on their own. A large facebook group is nice but has little direct influence.
What is allows is for those with more influence in the world of politics to use them as a tool. An extra piece of the narrative to keep a story running a bit longer, or an extra way to prevent a politician from dismissing it as unimportant.
Take today with the Alan Duncan gaffe (for anyone reading this after a fair amount of time has passed, I probably need to specify which one, it's the "MPs living on rations" thing he said to the journalist (from the magazine that'd previously dug a £ sign in his garden during the expenses scandal) that he'd invited to Parliament. On BBC News it was reported as "David Cameron has said he apologised and no further action needed" (paraphrased) but it mentioned ConHome as running a survey saying he should go.
In the era of strict party discipline the media is going to increasingly look to sites like ConHome or bloggers who the party has less control over for dissenting voices (and the media loves dissent in the ranks). With the added bonus that it's harder for leaders to shrug off apparent criticism from ethereal 'grass roots'.
The supposed grass roots revolution will happen, but I doubt it'll go exactly as predicted. We're not going to head towards some sort of direct democracy or grass roots control etc. I don't think there's much bite in these movements in terms of what they could or will actually do in terms of traditional methods of exerting influence, but the bark will be enough, the need to be perceived as not ignoring the grass roots that applies the pressure.