It's asserted with some frequency that using "liberal" as a political label carries with it too much baggage, and consequently those on the left have increasingly opted to self describe as "progressive" instead. In his syndicated column, Pat Buchanan recently made reference to this.
Living in the center of the country, thousands of miles away from the trend-setters on the coasts, I realize that I may as well be living in a time machine, but I have never noticed much in the way of execution of that label switching in my own personal experiences.
Via Google's Ngram viewer, take a look at the frequency of the terms "liberals" and "progressives" (used instead of "liberal" and "progressive" to avoid errant counting of non-political occurrences of the two words) in books published in the US over the last century:
"Liberal" enjoyed rapid ascension during the thirties and then again in the sixties, but the Carter Presidency and Reagan Republicanism put it back in its pre-hippie place. Since then, it's been steady as she goes. "Progressive", meanwhile, like "liberal", became a familiar enough term during the Great Depression and the FDR presidency. It has remained steadily so since then, but over the course of the last 100 years has never come close to supplanting "liberal" as the term of choice to describe those somewhere on the left end of the American political spectrum.