[joshvm]

I think what you're describing is cookbook territory, and perhaps there's a niche for that (though some languages like C or Python have a huge scope). I'd like to see a website that curated libraries with cool examples.

The problem with a cookbook, IMO, is that it doesn't really teach you anything about the language. You could write some really cool (short) image processing code using OpenCV, but would it really help you learn C++ or Python? I suppose you could pick the top 10 libraries/frameworks and go from there.

But.. on the exercise front, there are certainly nifty ways of solving problems in some languages that aren't available in others. Python, for instance, makes a lot of programming challenges very simple with the standard library. Similarly stuff gets a lot more readable if you use C++11 onwards.

I agree there isn't much point if you already know the language inside out (though it's useful to keep sharp), but if you're learning it can be a great way to discover useful constructs like Python's itertools.

[rtpg]

I think the idea is that the best libraries for a language rely on the good parts of the language, so using those libraries will help you discover those.

For example, you have jQuery, which will expose you to DOM interactions, callback-style programming and even promises.