This short book might be the worst written thing I've ever finished. That said, it's particularly interesting reading for our moment. Habermas wrote it to suggest what a critical theory would look like in a world no longer organized on strictly capitalist principles. As such, it is written against then prominent social scientific theories, including Luhmann's increasingly, bafflingly popular systems theory.
But that organized capitalistic world went away shortly after this was first published; then capitalism did its thing again. Now, of course, the world of government intervention and so on is back. Where to from here?
Habermas' approach is no longer tenable. It was tailored for a kind of organized capitalism which was still operated along class-war lines: capitalism had to be saved from revolution. Today, capitalism is not threatened by revolution (despite what Fox News would have you believe), but by its own dynamics and blind spots.
What is interesting is the idea that economic crises are displaced onto politics when government steps in to the economy. It seems likely that this will happen again. The next time the economy tanks, governments will be thrown out of power. But whereas Habermas argued that this was rational (since the crisis, on his view, is the fault of government), today economic crises are not the fault of governments; political turmoil is an ideological response to economic problems. Habermas thought the world was entering a post-liberal-capitalist society. It wasn't true then and it isn't true now. Instead, we have completely immoral governments taking over from completely immoral businesses. Business is driven by profit, government is driven by electability, and we all suffer.
Habermas' solution to all problems is to invoke communicative ethics. According to this, communication is possible only if there is rationality. Since communication is possible, rationality exists. It is also necessarily 'interested:' rationality leads to emancipation.
Parts of this project seem salvageable (especially the link between reason and interest). But the foundations are too wobbly.
A pretty good reading guide, only a few pages long, can be had at:

http://www.arasite.org/hablc.htm ( )