Is questions asked really a good metric? StackOverflow actively discourages asking duplicate questions, and all the easy newbie questions haven't changed in a while, it seems inevitable that certain technologies appear to decline. I feel like traffic to questions, searches or other metrics would be a better indicator.

In particular, is facebook api usage really in decline? I'd be very surprised. For language/platform specific technologies, I would imagine if there were a decline the market for devs would get less tight. I'd argue that days a vacancy is open is a much better indicator than even raw number of job postings.