I guess that if you are a self taught rails or django developer you will miss these kinds of things.

But it also depends on how far you want to learn. I have a friend of mine that started with django and for a long time, only knew how to push data back and forth a database. But after a while he slowly got in to these kinds of things(Big Os and mathy things) and now he is better than me at algorithms and optimizations(not that I am any good at that).