I've linked to it before and I'll link to it again: Roy's Station Coffee & Teas is a pretty awesome coffee shop.
It's right in the heart of Japantown at the old location of Roy's Mobile gas station (corner of 5th and Jackson), has a wi-fi connection that draws plenty of laptop users to the shop and always seems to have an interesting mix of people occupying it's smallish interior and spacious patio.
I like it because when I sit outside and plan for my Dungeons and Dragons campaign, I always catch snippets of interesting conversations. I find that a lot of professionals from the local businesses, realtors, SJPD, attorneys and so on meet at Roy's to conduct business in a casual setting on the weekdays, so the mix of conversation is cool.
Mind you I don't listen in to invade other's privacy. That would be hard to do at Roy's anyway because people there are on average older and universally more mature than what you'd find at a few other coffee shops I could name. This means if they have to speak about sensitive topics (or curse) they at least lower their voice.
It's fun too because I usually get to hear at least one other language besides English: often Spanish, sometimes others like Japanese, Korean or (today) Mandarin Chinese.
So I let the conversations happening around me come to my ears as they will, while I go about my work on my campaign.
If you're local to San Jose, live near downtown or want to explore new coffee shops and/or Japantown, give Roy's a try. It's a blast.
Oh, forgot to mention: straight up people watching at Roy's is a awewome too.