From Think Progress: More Americans have a positive reaction to ‘progressive’ than ‘capitalism.’
Despite Fox News host Glenn Beck’s conspiracy theory about progressivism being a “cancer” that is secretly plotting to destroy the country, Americans have a largely positive view of the word “progressive.” Meanwhile, “capitalism” appears to not have fared so well following the Great Recession. A new Pew poll of nine political words and phrases found that a strong majority — 68 percent — of Americans have a positive reaction to the word “progressive,” while only 52 percent have the same response to “capitalism”.

Of course, capitalism and progressivism are not opposites, but perhaps Americans view one as the cause of the economic crisis, and the other as the solution. ThinkProgress has noted that the tea party movement hasn’t proven popular in recent polls either, with socialism and even the Internal Revenue Service [[IRS) receiving more favorable ratings.
The "militia" numbers are interesting too.

Lately I've been curious about how word frequencies change over time. Does anyone know of any good websites that track such things? I'm not thinking of poll-based data like this story but more like web spiders that count word frequency in recent news articles, etc.

I know about Word Spy but that's focused more on emergent rather than existing words.