We’ve just received word that Walt Mossberg has collapsed on the sidewalk outside Yerba Buena. That’s all we have at the moment. One minute he was standing there doing a monologue about the tablet and raving about how amazing it is and not letting anyone else get a word in edgewise — and then bam. He went down. Katie B. (in photo with Walt) has called for an ambulance. Kara Swisher immediately posted the news and then began monitoring other blogs to make sure they credit her with the scoop.