This November 7 New York Times article says that turnout expert Curtis Gans believes between 126,000,000 and 128,500,000 voters voted in this election. But Professor Michael McDonald, another turnout expert, estimates 133,300,000 voters voted.
In 2004, the number of valid votes cast for president was 122,295,345. But in 2000 it was only 105,396,627. It thus seems clear that the 2004 election, not the 2008 election, had the more dramatic increase over the preceding election.