Actually most of them. It's pretty easy to eliminate them if you have the hostname entry from the scan and cross-reference with public distro mirror lists. Also exclude any edu servers and names of universities etc. If you want to look for actual files, there's hardly anything better than http://filemare.com. Crawlers like Napalm (http://www.searchftps.net/) focus more on servers that are meant to be public. Using filemare one can find the interesting things ;-)