I grew up in Palo Alto. There's 3 options that come to mind:
* Happy Donuts on El Camino, which is open 24/7 and often is filled with geeks coding at all hours. Lots of people are happy to talk and socialize / be engaged in conversation.
* The downtown PA bar scene: Rose and Crown & Rudy's are probably the most geek-friendly. Old Pro is ok if you're also into sports. Blue Chalk & Nola can be good hangout spots but I wouldn't label either of them first choices.
* California Avenue has Antonio's Nut House. Lots of notable geeks can be seen there. I heard [redacted] was mobbed the last time he went in.
Going to San Francisco sucks unless you already know where you can sleep. I recommend making friends with some local residents and crashing with them after going out (with them). I actually met a dude on HN and we've been out partying in SF a few times; I crashed on his couch a couple times and it's been real sweet.
I also recommend Hacker Dojo, which is open late if you're a member, or 'til 10 if you're a guest, and they've been having some nighttime weekend talks recently.
Finally, I recently moved back to the area after growing up here, and would like to make some more friends, especially tech & business minded people. Contact information is in my profile. I would love to buy you the drink of your choice at any of the above-mentioned venues and hear about what you're working on.