This is a very popular subject in several forums. I know a lot of the things you people have said. I'll even relate an apocryphal story.
In 2003, I had basically been out of work or under employed for two years after moving back from Antigua to San Diego hoping to get work closer to the ocean rather than where I live now in Austin Texas. So after I lost a job I had been in for just three month and since the wife wanted to be back in Austin I decided to drive back. I had an old ranger that my dad gave me after my car was stolen (it was a bad couple of years). I filled up the back of the ranger with a bunch of furniture and stuff, then filled up the boat with even more stuff, then proceeded to drive to Austin. For some reason although I was pulling the boat with a 2.2 liter ford ranger, I thought I should drive close to freeway speeds climbing the mountains east of San Diego. Needless to say on some of the steeper grades I was only able to do 20 miles an hour. When I finally got to the other side of the mountains I noticed a lot of smoke pouring from the back of the truck. When I finally pulled over I found that it had hardly any transmission fluid left. I topped up the transmission fluid, had it checked in Tucson, and drove on to Texas.
I was fortunate in that it wasn't for another six months, right after I finally landed a job that the transmission went out.
So needless to say, I already know the answer to my question.
Also note that I have driven through Arizona, California, Texas, Wyoming, Washington state and elsewhere. From time to time I have seen a camper pulling a car pulling a boat or a truck pulling a camper pulling a boat. So I know it can be done. Legality is another thing altogether. I am also (for this discussion) not so worried about the wisdom of doing so. I'd be really interested in hearing about successes and spectacular failures