Problem with just logging the progress is that the user has no idea where he "bottom" is. A log might as well be a spinning cursor or any other animation.
This is the most infuriating part of progress bars to me. When it hangs I don’t even have a jumping off point for Google. I can only search “foo hangs during install” which almost always results in issues that are not the problem I’m experiencing because usually the most common reason isn’t the reason the majority of the time. “Foo hangs during ‘reticulating splines’” usually has far more useful results.