There are a number of "synthetic" fuels being tested, but herein lies the difference...

The USAF is proving that its entrie fleet can be flown using jet-fuel made from converted coal. I can't remember the name of the process. You essentially end up with Jet-A that was made by cracking coal. The US has, I believe, the largest coal reserves in the world.

Virgin flew a 747 (only one engine used the bio-fuel) that was made from coconut oil. It worked, but is for all practical purposes, a publicity stunt. Coconuts grow too slowly and do not produce great enough density (biomass per acre) to be economically viable. And think what would happen to the price of Coppertone if all that coconut oil started going into jet engines...

CAL and Air New Zealand flew jets (again, I think only one engine used biofuel) on Jatropha-based fuel. Jatropha is interesting because it is a weed that will grow just about anywhere. Its density and regeneration are such that it can produce a significant biomass for conversion, and requires almost no cultivation (hands-off farming).

Thawednook, I too read that Jatropha Biofuel (I will call it "Jet-J" from now on) has a lower freeze point than Jet-A. It's an issue on long flights, such as the polar flights from the US to Asia. My one experience with it was in a 747-400, and our fuel got down to 3 degrees above the freeze point--the limit before you have to change course, altitude, or speed.

What isn't addressed is the "lubricity," or effectiveness of fuel's lubricating properties, as the temperature drops. This is important in systems such as fuel pumps. Just because the fuel isn't frozen doesn't mean it still is lubricating the pump. This probably still requires research for Jet-J.

In all these alternatives, proof that it will work doesn't mean it is economically viable. Can't remember exactly, but seems the USAF's cracked-coal (Jet-C?) costs over $50 a gallon to produce, in its current limited quantities. Other biofuels are also currently very expensive.

For the near future (I would estimate 5 years) biofuels will be big news items, but it won't become significant until it is cheaper than petroleum-based fuels.