According to the USGS (Figure 1), 238,000 people near the quake's epicenter experienced violent to extreme shaking, capable of causing very heavy damage. A further 3.2 million people experienced very strong to severe shaking, capable of causing moderate to heavy damage. Another 1.3 million people experienced strong shaking, capable of causing moderate damage. Haiti's total population is just 9 million, so half the country's population lived in areas that received moderate to very heavy damage from the earthquake.According to the BBC, the destruction is overwhelming in the area of Port-au-Prince. The Parliament building collapsed, along with some large percentage of structures in the capital. The Prime Minister believes more than 100,000 people have died, or are now dying, in the rubble.
This is the sort of disaster that can have really long-lasting effects. Of course, Haiti was already poor (though it had recently been showing signs of life), but this obviously increases the impact of poverty for millions of people, so many of whom must now be homeless and without jobs. And if the death totals are as high as the Prime Minister believes (or as high as one Haitian Senator estimated, at half a million), the number of disrupted families and communities, and the number of orphaned children, are on the scale that can have negative repercussions for a society for generations.
Oxfam would be a good place to donate to the recovery. The Map Room has more map links for the quake.