FWIW, I've decided not to make much out of incomplete downloads as long as they stay minimal. Heck, a really good top of the page could have someone clicking into the site really fast, and stopping a download midstream.
I never thought much about it until I had a server that was kinda slow once. A client was running this huge piece of portal software that was bringing the system to it's knees. I started noticing all these reloads and figured out what the problem was.
I don't think you can target incomplete loads, more just reloads. As long as you aren't doing dynamic content or anything that would nix browser caching, I think you can put some stock in the numbers. I normally run about 2-3% of the requests as reloads. It runs lower on the sites with larger pages, and runs lower on smaller paged sites. Sites with heavy external js run upwards of 5% to 7%, while sites with Java applets can run as high as 15%.