[hoggle]

This is an opinion: Go get http://eloquentjavascript.net and build something useful in plain Javascript/HTML5 (no jQuery yet, it might harm your successful picking up of the language!).

The fun part is that you can get started immediately: http://jsfiddle.net

For HTML/Javascript references you can always prefix your google searches with "mdn" to access Mozilla's excellent documentation on all things web e.g. "mdn html5 canvas"

If you feel like you really need some server backend logic look no further and also stick to Javascript and checkout node.js (with express.js).

There will always be some new things on the horizon but don't get distracted by the newest go, erlang, ruby, etc. based web framework and no not even Meteor nor Derby even though they are Javascript based.

Plain Javascript (and node.js) are very much here to stay (and also fun!).

I guess my answer to your question is to really focus on a certain set of technologies in order to acquire some deeper knowledge by constantly applying it to something which actually gets used regularly.

In the end it's about helping/entertaining other people by shipping stuff.