Any good developer would say they don't keep up with technologies: they just pick the ones that apply to their work. You don't need to study Hadoop 'just because', you study it because it would help you in your work dealing with 'BigData'. Stay away from hype and focus on work.
If you're trying to study concepts, it's a different case. You study the concepts, not specific technologies.
An example would be MVC. There's a lot of MVC frameworks that's out there. If you want to pickup on MVC, just choose among the MVC frameworks - Groovy/Grails, C#/ASP.MVC, PHP/CakePHP, Ruby/Rails, etc. etc. again, stay away from hype and language/framework vs. language/framework debates. If you pick one you're comfortable with, the concepts transcend language and time. If your career moves you on to another language, you'll find MVC is 'almost' the same save for minor differences that is brought upon by the languages themselves.
Especially applicable for the number of JS MVC Frameworks popping up every 3 or so months.