Just because something isn't used in your every day new code doesn't make it unimportant. I haven't used any friend classes, but we have guidelines on how to set them up and I am fairly certain there are a few of them at the key points in the infrastructure.
Deprecated features, on the other hand, such as the bool increment, are indeed perfectly avoidable.
I have learnt this feature. I only intention is to prepare well for interview as I am in finance industry and want to move into C++ . I now want to master the areas that will be more useful for me and therefore asked this question.
Finance is large. The people who program order management systems, guaranteed delivery messaging queues, financial risk calculations, or, to take it to the top, high frequency trading implementations, are all doing completely different things.
I don't know about everyone, but we, for example, expect the junior hires to know and understand Effective C++/Effective STL, among other things. Those books probably make for a good preparation material for any entry level C++ job.