Like many of my colleagues in Silicon Valley, I was having a fantastic day today. It is crisp in the shade, warm in the sun. The skies are a magical blue with puffy clouds floating like dreams. And when all seemed to be going well, an email in my inbox — without as much as the new message sound — arrived: Letter from Steve Jobs. It was as if the inbox was observing the solemnnity of the occasion. It is an end of an era.