This is a very interesting topic that I have been following for the past few days. I am not a chemist but I did work as a lab technician for several years, in the area of various types of solvents. Not being a chemist, I may not have everything absolutely 100% correct but I will offer my 2 cents worth anyway.
Several points have been made about toluene damaging the paint, being very flammable, it's ability to increase octane, etc. Toluene is a very good solvent which I have used many times to remove glue, old tape adhesive, etc. All solvents may damage a painted surface under the right conditions but toluene is not a paint remover. I wouldn't wash my car with it but a few drops on the paint will probably not damage the surface, assuming that the car didn't come out of the paint shop yesterday. If you do get some on the paint, do exactly the same thing as you would do if you spilled gasoline on the car. Wipe it off as quickly as possible and rewax the area since the wax has probably been removed.
Flammability is another issue. We are talking about a hydrocarbon solvent here, and we are going to mix it with gasoline. Both are extremely flammable and should be handled with care. I don't believe that toluene is any more dangerous to handle than gas. The flash point for toluene is 10 degrees C in a tag closed cup but while I couldn't find any data on gasoline, I would imagine that it is about the same or possibly lower. Let's face it, we are talking motor fuel here, be careful.
Toluene is a pure compound. That is to say that all of the molecules are the same. Gasoline is a blend of many different compounds that is produced in high volume to give certain characteristics when burned in an internal combustion engine.
One of the compounds typically found in gasoline is toluene. Xylene and benzene are two others, and the three are very good at increasing the octane but there are other factors involved. The refiners want to keep costs down and these three compounds are relatively expensive and can also be purified and sold for other uses. Additionally, benzene is a known carcinogen, that is one reason why gas pumps in California (and other areas) have the cancer warning sticker on them. I believe that the refiners have tried to reduce the amount of benzene in pump gasoline. It addition to the hydrocarbons in gasoline, the refiners also add various additives to boost octane, clean fuel injectors, etc.
There have been quite a few references made to lacquer thinner. Thinner is a blend of various solvents but there is no way to know what the producer blended unless you inquire. Toluene may, or may not, be in the blend. Lacquer thinners often contain esters, ketones, alcohols, and other hydrocarbon solvents such as toluene. If you think toluene is hard on your paint, try rubbing the paint with some lacquer thinner that contains acetone or ethyl acetate. Same goes for rubber o rings, hoses, gaskets, etc. Maybe one brand of thinner will not hurt them, but another could make a mess. Be careful since you don't know what is in the thinner.
So to sum up, toluene is a very good octane enhancer, it is a good solvent that may harm a painted surface, it is very flammable, it is found in most pump gasoline, and be careful using thinner.
I hope that I haven't made too many errors
Regards,
Wayne