Ask HN: How do you determine what technology or language (if any) to learn next?

To keep up with the frenzied pace of tech change (see JavaScript), developers need to keep learning. I consider myself a pretty experienced and capable developer, but almost every day I learn about a technique, technology, or language that seems relevant to my work or future employment prospects. It is simply not feasible to attempt to learn it all, and some technology might even go out of fashion in a short time. So I might prioritize what I learn based on such factors as learning curve, closeness to my existing knowledge, potential ephemerality, what other devs are learning, etc. How do you allocate your scarce time to learning new stuff? How do you identify what is worthwhile to learn, and in what order?