Burned by the 2006 election, Denver voters overwhelmingly voted by mail or in early voting centers in 2008.
Election day turnout was only 42,634 voters. There were 50,734 voters who voted early. There were 171,102 mail-in ballots returned. Including a few dozen "emergency ballots", there have been 264,513 votes counted this year. Just one in six of those who voted this year in Denver voted on election day, many of whom voted in the morning. Thus, the traditional activity of rounding up people who haven't voted after the morning rush of voting is over, and getting them to the polls on election day was less critical this year than most years.
Denver has active registered voters 312,907, and 102,901 inactive registered voters. Turnout was 84.5% of active registered voters, and this may swell slightly as provisional ballots and considered and counted. Most provisional ballots in Colorado end up being counted.
Based upon my experienced canvassing on election day, it is fair to say that a significant number of active registered voters who didn't vote on election day (as well as most inactive registered voters) no longer live at the addresses where they are registered to vote. Probably more than nine out of ten voters whose registrations are accurate voted in this Presidential election in Denver.