I don't think it's any kind of a solution, especially not the way i tis currently being pursued. In particular, turning food-crops into ethanol is not any kind of a solution. Given that we need food, and growing food is an energy-consuming process, it seems obvious that eating it is the most carbon-efficient use for food. They got away with it in Brazil because, unlike most countries, they have a conjunction of large amounts of productive land not required for food production and cheap labour; and it was also until recently a better strategy than producing food for export because until the recent past food was unnaturally cheap because so many countries were subsidising its production. I was going to say that at the moment Brazil would probably do better turning some of those sugar cane plantations over to food crops such as rice and maize, but then I remembered that bio-ethanol for fuel is also unnaturally over-priced at the moment.

Turning waste materials (including especially the inedible part of the food crop) into ethanol could be part of a solution, but I suspect there is a better net carbon outcome for either or both of:
(a) burning the waste material directly in an electricity generator
(b) composting the waste and using it as fertiliser, burning any methane generated in composting.

An important issue is that liquid fossil fuels are just brilliant for use in transport, and it is much easier to decarbonise stationary fuel usages. As long as we are burning fossil fuels for non-mobile uses, it makes sense to use the fossil fuel for the transport and the low-carbon alternative in the non-mobile use. Trying to decarbonise transport by regulation and (worse) by subsidy before the stationary fuel consumers is an unnecessarily expensive method of decarbonising.

After waste, the most efficient agriculture for turning biomass into useful energy is to grow carefully chosen crops, such as elephant grass, which are suited for burning in generators. Even then, when you work out how much land you need to make any kind of impact on our energy needs on a global scale, you soon work out that there just isnt' enough surplus productive land on the planet to make much difference. Biomass will play its part, as it already does in many less developed countries, but it is not a panacea for decarbonising the main carbon-consuming parts of our economy.

All this talk is getting me more and more hooked on converting my lawnmower to burning wood, (it's the only internal combustion engine I have at the moment).

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And the "driving on the freeway on a scooter" analogy still holds true because the pilots are sitting in 7 to 30 ton aircraft o' doom and you are running around them in your very own Meatbody, Mark I. Beep, beep.
Trying to make sense of computers, The Error Log.

So you've got steam engines running everything else?

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We want our children to go to the planets. Burt Rutan 6/21/04
Tuckers! Science! Automotive Oddities! Boycott Trek XI! Building my hot rod with the help of the intarwebs Those who would delay scientific progress for a little temporary prosperity shall have neither. MachineCast

No, it's the only engine I have or any kind, and the conversion to wood burning won't be to steam.

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And the "driving on the freeway on a scooter" analogy still holds true because the pilots are sitting in 7 to 30 ton aircraft o' doom and you are running around them in your very own Meatbody, Mark I. Beep, beep.
Trying to make sense of computers, The Error Log.