I read James Carroll's House of War a while ago and he stated that post-war analysis of the allied strategic air campaign in WW2 showed that it was a failure.
His argument seemed to be that the campaign proved self-defeating as it failed to prevent (overall) effective mobilisation (i.e. wasting allied resources that could be more profitably employed) of industrial resources and often indirectly supported them; he cited an example of civilian workers loosing their employment due to city centre destruction and being forced to work in war industries instead i.e. indirectly mobilising more manpower for war industry.
How accurate is this; was the campaign actually ineffective?
I would argue that the strategic effects of the bombing of germany's oil and avation fuel helped tremdously. Here is a qoute from the american report concerning the strategic bombing campaign after the war.
"The German oil supply was tight throughout the war, and was a controlling factor in military operations. The chief source of supply, and the only source for aviation gasoline, was 13 synthetic plants together with a small production from three additional ones that started operations in 1944. The major sources of products refined from crude oil were the Ploesti oil fields in Romania and the Hungarian fields which together accounted for about a quarter of the total supply of liquid fuels in 1943. In addition, there was a small but significant Austrian and domestic production. The refineries at Ploesti were attacked, beginning with a daring and costly low-level attack in August 1943. These had only limited effects; deliveries increased until April 1944 when the attacks were resumed. The 1944 attacks, together with mining of the Danube, materially reduced Romanian deliveries. In August 1944, Russian occupation eliminated this source of supply and dependence on the synthetic plants became even greater than before.
Production from the synthetic plants declined steadily and by July 1944 every major plant had been hit. These plants were producing an average of 316,000 tons per month when the attacks began. Their production fell to 107,000 tons in June and 17,000 tons in September. Output of aviation gasoline from synthetic plants dropped from 175,000 tons in April to 30,000 tons in July and 5,000 tons in September. Production recovered somewhat in November and December, but for the rest of the war was but a fraction of pre-attack output. "
Here is a link to that american report concerning the strategic bombing campaign after the war. It was written in September 30, 1945, so while it doesn't have year of analysis, it is a very good place to start
Generally, the strategic air campaign in both major theaters was wasteful at best. did it have marginal impacts - of course. Did it materially shorten the war? Probably not.
German industrial production peaked in 1944, after four years of increasing strategic bombing. Eisenhower threatened to resign in early 1944 unless he was given operational control of the bomber force to support Overlord. The USAAF was violently against that. The European war ended because the Russians bled the Germans dry. The strategic bombing in reality was simply terror bombings of the cities. The Eighth Air Force had more casualties in Europe than the Marines did during the entire war.
In the Pacific, the Navy was starving the Japanese home islands through the destruction of shipping. A key objective of the island hopping campaign was to secure bases for the B-29. (The B-29 program cost more than the Manhattan Project.) The B-29 was only 'effective' as a terror weapon when it fire-bombed Japanese cities. The atomic bombs did indeed shock Japan into surrendering and undoubtedly saved hundreds of thousands if not millions of lives.
Did the strategic bombing campaign contribute to winning the war? Yes, to a minor extent and the individual sacrifices and heroism of the aircrew should not be diminished.
A final note: the strategic air campaign was used to justify separate air forces, and was founded in large measure on air power theorists (Guilio Douhet, among others), who maintained that with a sufficiently large air force that ground armies and navies were no longer necessary.