I'm with you, it's a cool idea, but a.) the UI is somewhat lacking - it's not obvious how to access information or confirm/refute posts once you've found them, and it seems generally to emphasize form over function, and b.) I'm not entirely convinced that this will be that much more accurate than existing methods of information sharing. Certainly placing an emphasis on confirming/refuting claims rather than just spreading them regardless of their validity will help, but let's face it, people are unreliable. It doesn't seem like Grasswire could've stopped something like reddit's Boston marathon fiasco, for example - with that, there was a large group of people that agreed on something totally false. But that's not to say I don't like it - I do think Grasswire is at least a step in the right direction.
Ryan Holiday had a poignant comment on the Bin Laden assassination. It's been trumpeted that Twitter broke the news of Bin Laden's assassination ahead of traditional media, therefore Twitter is the shiznit. Mr. Holiday pointed out that Twitter beat the official announcement by seven minutes. There isn't a lot of news where seven minutes matters. You'd much prefer fact-checking and vetting. What we need is a combination of grasswire, factcheck.org and Snopes.