I moved to SanFran with my girlfriend without knowing anyone about 8 months ago. I live in between the Mission and Noe, on Guerrero St. I still don't really know anyone outside of my job but it's a great area full of friendly people. You can easily strike up casual conversation with most people in Doloros park. I joined a couple meetups and met some good people but then got to busy at work and haven't attended any in a while. There's noisebridge on Mission St where you could go hang out and meet some people. https://www.noisebridge.net/wiki/Noisebridge

My view is that people in the bay area are very friendly and it's reasonably easy to make friends (accounting the geek factor ;-). A good start is to check meetup.com for groups with similar interest (startups, programming languages, food, etc). If you're into hiking, the Stanford Outing Group is pretty good:

https://mailman.stanford.edu/mailman/listinfo/outing

They are not affiliated with Stanford anymore and they have user-organized group hikes regularly (sometimes every week) around the bay area.

The Height and nearby neighborhoods like Cole valley and inner sunset are fun, central and have plenty to do. That said there is no shortage of geek socialization opportunities (meetups, etc.) seemingly every night of the week.