The conclusion is, basically, that speed reading courses don't work.
You can teach people to skim at a faster rate than they'd read with maximum comprehension and retention. And you can teach people study skills, such as how to summarize salient points, and take notes.
But all these skills are not at all the same as what speed reading usually promises, which is to drastically increase the rate at which you read with full comprehension and retention. According to Carver's book, it can't be done, at least not drastically past about the rate you'd naturally read at the college level.
Check out the book for a much more comprehensive explanation and analysis.