Turn-out estimates are vague, but obviously substantial, to judge by the statements "Tens of thousands of protesters fed up with government spending marched to the U.S. Capitol on Saturday ..." and "The line of protesters clogged several blocks near capitol, according to the D.C. Homeland Security and Emergency Management Agency." I take that to mean "a whole lot of people showed up." If I remember right, the D.C. authorities have stopped releasing crowd-size guesstimates in order to avoid ruffling feathers, so we'll just have to work with the post-protest claims and counter-claims by supporters and opponents.
Perhaps the most important paragraph in the piece is the following:
Many protesters said they paid their own way to the event — an ethic they believe should be applied to the government. They say unchecked spending on things like a government-run health insurance option could increase inflation and lead to economic ruin.That not only underlines a major motivation for the protest, it undercuts charges that the day is an exercise in "astroturfing."
It sounds like the event is staying reasonably on-topic, with opposition to expanding the role and expense of the state.
Nice take here from the Washington Post:
The groups behind the protests include a broad array of self-described libertarians, independents and other factions, who have emerged as a force largely independent of GOP leaders in Washington. Some of that is by design: Leading activists among the conservative groups say they remain suspicious of a party that endorsed runaway deficits, a Wall Street bailout and other Bush-era policies they found objectionable.The media seems to have moved beyond the claim that this is some sort of fake protest, to growing concern that the peasants really are revolting without any insiders at their head.