Marx's concept of alienation involves a somewhat different kind of separation and breakdown -- separation of the person from his/her nature as a free producer and creator, and separation of the person from his/her natural sociality. Marx thinks of affirming social relations as founded on equality and freedom. So modern capitalist society is destructive of true sociality.
What is interesting in this comparison is that both Durkheim and Marx appear to be diagnosing a similar feature of modernity. In Durkheim's case there is an implicit contrast between a pre-modern world in which individuals have a well-defined social and moral place and the contemporary world in which these strands of solidarity are breaking down. In Marx's case the contrast is forward-looking. Marx compares the present -- the factory -- with the future -- a society of free, equal, social producers. But in each case the theorist is grappling with an absence in modernity -- an absence of a social and moral setting that gives the individual a basis for self-respect and sociable collaboration with others. The social itself is breaking down. (This is a theme with other social theorists as well; for example, in Tönnies' distinction between Gemeinschaft and Gesellschaft. Peter Laslett's title The World We Have Lost, England Before the Industrial Age captures some of the same idea.)
Coming forward to the social theories of the late twentieth century, these issues continue to fascinate some social observers. Robert Putnam's work on trying to measure the changing density of civic involvement (social capital) is a different perspective on Durkheim's concept of solidarity. (Another great title -- Bowling Alone : The Collapse and Revival of American Community.) Sociologists who focus on disaffected young people are raising similar issues. And the New Left sociology and theory of workers' alienation from society picks up where Marx left off on this issue.
Is the time right for a new round of thinking about the nature of social consciousness and social solidarity? Do we need some new concepts of how ideas and identities contribute to a social whole? Is the study and theorizing of social subjectivity an important aspect of the challenge of sociology?