This article from America in WWII Magazine sums it up pretty well. Most were assisted by friendly Chinese civilians/guerrillas (it's not clear) who had ample reason to be anti-Japanese. Two planes' crews were captured by the Japanese. One plane had to ditch near Vladivostok, Russia, and its crew was detained by the Soviets and apparently escaped through Iran! If anyone knows more about that bit (bolded below), I'd love to hear it.

Here's the excerpt from the final few paragraphs:

Due to the raid’s extreme secrecy, plus the usual confusions of long-distance wartime operations, no real preparations had been made to receive the planes in China. “In the end,” writes Craig Nelson, “the airfields were never arranged, inspected, or supplied as planned, and the boys, already flying on a prayer, would find that some prayers go unanswered.”

Planners in Washington, DC, also had made a ridiculous blunder, forgetting that the ships would lose a day (April 14) crossing the International Date Line, putting the planes in China a day earlier than anyone expected. Because of this mix-up, when some of the bombers flew over Chuchow Field, which was supposed to have been their main refueling base, an air raid alarm sounded and the lights turned out.

Ultimately, 11 of the crews had to bail out and sacrifice their planes. As navigator Thomas Griffin of plane 9 said, “The bottom hatch was opened and one by one we eased down through the black hole into nothing. Jumping at night and in a storm is an experience one will never forget.” Only Doolittle had ever parachuted before (twice), but with a few exceptions—a broken shoulder, foot, or kneecap, and sprained ankles—all but one of the others reached the ground safely. Leland Faktor, engineer-gunner of plane 3, was killed in the fall.

Four of the other B-25s crash-landed, three in the water and one in a rice paddy. Crew members from planes 2 and 5 emerged safely, but William Dieter and Donald Fitzmaurice, the two enlisted men on plane 6, drowned just off the China coast. Four of the five crewmembers of plane 7 were hurt seriously, and pilot Lawson’s leg had to be amputated in the field by Thomas “Doc” White, plane 15’s gunner, who had graduated from Harvard Medical School.

Plane 8, low on fuel its entire trip, made its way to near Vladivostok, Russia, instead of China. The crew members landed safely, but were interned by the Soviets for more than a year before they escaped over the mountains into Iran in late May 1943.

Eight raiders, the surviving crew members of planes 6 and 16, were soon captured by the Japanese. Three were executed in October 1942 following a sham trial, one died of malnutrition in prison, and the other four continued to live under horrifying conditions—torture, disease, solitary confinement—until they were rescued in August 1945. (One of these last four—plane 16’s bombardier, Jacob DeShazer—would return to Japan after the war and spend 30 years there as a Christian missionary. Born in November 1912, he is the oldest surviving raider.)

With the help of locals in China, most of the raiders on the ground made their way to safety and were soon back in action. The city of Chungking had been bombed by the Japanese more than 100 times in the preceding decade, and the Chinese were delighted someone had returned the favor to Tokyo. But the Japanese wanted revenge for the revenge, and went berserk trying to strike back at everyone who might have assisted the raiders. They slaughtered as many as 250,000 people. “We heard stories far too brutal and savage to relate,” two Catholic priests told the New York Times in May 1943. “Just one charge was not heard—cannibalism.”

In all, 10 raiders died during World War II. Four escaped the Japanese only to end up in German prisoner-of-war camps. Today, 65 years after that clear April day over Japan, 15 of the 80 survive. They range in age from 84 to 93 years old. They are a true band of brothers, still meeting annually to talk over old times and celebrate their remarkable achievement.

Two days after the raid, Doolittle stood next to his wrecked B-25 on a hillside in China. He had no idea what had happened to his other 75 raiders. The attack was “a complete failure,” he told Paul Leonard, his engineer-gunner, adding that the air forces “will never give me another plane.” He thought he would be demoted and possibly even court-martialed and sent to prison. Leonard disagreed. “When you return home,” he said, “they’re going to make you a general. And then they’re going to give you the Congres-sional Medal of Honor.” That’s exactly what happened.

EDIT: Fixed formatting.