* They are the first Q&A site I've seen that is completely personalised - you only see questions that are either followed by your social graph or apply to the topics you have selected.
* Questions are owned by the community, not the person who asked the question. It's actually pretty hard to figure out who asked a question in the first place, and other people can improve the wording, apply topics etc.
* They don't use a dumb points or badges based incentive system. Instead, their incentives are much more subtle - it's all about seeing how your peers respond to your interactions. The "thanks" button is a lovely example of this.
In 2002, would you have said "There's nothing innovative about Google in terms of technology or concept. It's a search engine. No more, no less." ?
But I don't think they're a "blogging" innovation. That's just a catchy headline.