Abdullah is alleging massive voter fraud, including ballot stuffing, and he claims to have video evidence. But he's also urging calm and calls on his supporters to refrain from violence.
Voter turnout may be as low as 29%, because of threats of violence from Taliban forces and because many Afghan voters doubted the legitimacy of the elections.
It will not be until September 3 at the very earliest that we'll know who won the election.
Abdullah, an ophthalmologist, is a former member of the Northern Alliance. The bulk of his support is in Afghanistan's population centers, and he is basically a big fat smarty-pants elite intellectual reformer. He would like a parliamentary system instead of a strong president, elected officials in the provinces and districts instead of corrupt and ineffectual appointed officials, and other liberal nonsense.
He also promised to curb the rampant corruption and review foreign assistance programs to ensure that they focused on grass-roots development and addressed poverty and unemployment. In his public meetings, he emphasized support for the rights of women, the unemployed, the disabled and the victims of war.
If Karzai receives less than 50% of the vote—which might depend on how much the vote was fixed or on the incredibly poor turnout—there will be a runoff. Also lots of people and things will be blown up and killed.