You can hear about the big names and hot companies in the Silicon Valley, but if you want to feel it happening, come by Castro Street in Mountain View.
Go on into the Red Rock Cafe and head up the narrow stairs to find people plugging away on their laptops, working and talking together. This is where they come to informal working groups, Meetups, like those for Android App and IOS (apple/Mac) developers. This is where it's actually going on.
History is happening here.