60-70K is more reasonable, but I'm more dubious of impact than Silver for the reasons I gave previously. That is to say, the protesters represent a known group of the 30% or so of the electorate who absolutely oppose Obama and the Democrats generally. In market terms, their opposition should be discounted because it was already factored in to the existing price. It is the same reasoning that prompted the Bush Administration to discard much larger protests before the Iraq War. They concluded that the protesters were entirely from that segment of the population unalterably opposed to their Administration, and therefore could be safely ignored (in the short term).
What is bad news for the Ds is the decline in fervor in their own ranks. The Ds won handily in '08 (and '06) not only because the Rs had lost tremendous support. They also were successful in mobilizing their own base.
This, as always, is the piece the Ds miss. In many of the districts that flipped in '06 and '08, I predict that very few voters will flip from R to D (a reversal of the 1994 dynamic, which saw significant "re-alignment" of voters who had voted D for historic reasons). OTOH, I predict serious mobilization problems for the Ds in these districts -- and generally. There is no energy in the rank and file at this point, and the "permanent structure" for the 50 state strategy developed by Dean is being allowed to wither. The DNC has mde no efforts, as far as I can tell, to maintain relations with its ground troops. It is not clear to me how they expect to mobilize them again in January.
This becomes especially urgent for Ds if, as expected, the Supreme Court overrules campaign finance limits on corporations. The '06 experience demonstrated that boots on the ground could overcome financing advantages. Without boots on the ground, the Ds can expect to get creamed on fundraising as financial interests would rather have Rs than Ds in charge (for all that Ds have courted them and shown willing to play nice).