Questions about Alienation

Here I am speaking of the Marxist interpretation.

What is Alienation?
How does it affect workers?
How does it affect society at large?
Why is alienation important to a Socialist movement?

Alienation is derived from a theory of human nature which Marx formulated in his Economic and Philosophic Manuscripts of 1844. Basically, the theory contends that bourgeois social relations are fundamentally at odds with our innate nature (or 'Gattungswesen'). Alienated labor, for instance, is summarized well in the following passage:

"The alienation of the worker in his object is expressed according to the laws of political economy as follows: the more the worker produces, the less he has to consume; the more value he creates, the more worthless and unworthy he becomes; the better shaped his product, the more misshapen is he; the more civilized his product, the more barbaric is the worker; the more powerful the work, the more powerless becomes the worker; the more intelligence the work has, the more witless is the worker and the more he becomes a slave of nature."
Marx, Karl. Writings of the Young Marx on Philosophy and Society, p. 291.

The inequality capitalism engenders also prevents most people from fully realizing their innate potential. Broadly speaking, however, alienation negatively impacts humanity as a whole, not exclusively the working class. This short video is quite instructive on the subject: