I didn't, it was pretty hand-wave-y. But I do know a fairly large number of people in the Bay Area tech scene so I took stock of what they were saying, in particular around hiring difficulties. Also, I did some tinkering with the things that seemed to have merit from a supply/demand perspective and stuck with the ones that I enjoyed most.

One other thought: Coursera classes are an excellent way to give yourself an additional bit of edge in terms of getting the interview. Taking and doing well on Andrew Ng's Machine Learning class, for example, doesn't necessarily mean that you can do ML vocationally, but it does speak to your willingness and interest in continuing education.

Go to local meetups. You'll see the supply and demand play out right in front of you. How many employers are there, and how big of a group of potential employees are they talking to?