Well, that’s a bit of an impossible question, given the variety of political opinions, and the inherent vagueness of everday language.
In the U.S. there’s no formal ‘Liberal’ organization that defines what the word means, nor is there a single formal ‘Progressive’ organization that sets out defined policies and stances.
As far as general use goes, progressive and liberal are generally used to mean more or less the same thing. If I had to draw a distinction, I’d say progressive is generally more left wing than liberal (but not as left-wing as radical), but not everybody is drawing that fine distinction.
From what I’ve seen (as one who doesn’t identify himself as either and who is generally disgusted with politics in general, especially in this election year…), it seems that “progressive” is a lablel one uses on oneself, while “liberal” is what the other side calls you, often with a sneer. Both are to the left. I could be wrong on specific usage. I lean more to the right myself, when I bother to see where my opinions register on the scale. As for the “conservative” and “neo-con” label thing, beats me. I’ve been wondering that myself.
The word “liberal” has been polluted by the Republican party for the last 20-some-odd years (must notably from Newt Gingrich’s list of political attack words), to the point where its primary use in American politics today is as a slur. To get away from the negative connotations of the word, then, “Progressive” is now being used as an alternative, though I suspect that will only last until it, too, gets sufficiently smeared.
“Conservative” and “neo-con”, however, are another kettle o’ fish. While “conservative” remains the same as it has been for the last thirty years, the neo-conservative movement is a relatively recent growth, whose views can be cynically summarized as “The US is the world’s sole superpower, so we can do whatever we want and everyone else can get bent.”