Hyped up technology that went bust/ nowhere - your experience and advice

I'm sure some of you have had the experience where this 'up and coming technology' is being heard everywhere (even surfacing in job advertisements), and for some reasons, you felt compelled (or almost compelled) to invest your time to learn and see how it could be used.

Turned out, the technology never did go off (or it did, but died quickly, or 're-branded' as something else).

Any experiences, advice (on how to deal with this sorta hype-train) and lessons learned are much appreciated!