We just had "interesting" experience with the site www.hosts-file.net. They publish the hosts file with the list of more than 45k sites. This list can be merged with users hosts file to prevent them from visiting these sites.

Here are some examples of what they block:
www.adaware.com – lavasoft page which leads to one of the most popular free spyware remover AdAware.
www.authorize.net – one of the biggest credit card processing centers
www.looksmart.com – well known Search engine for commercial results
www.kanoodle.com – another search engine for paid results.
www.linkshare.com – an affiliate network
www.registryline.com – known rentals site
www.noblepoker.com – well know online poker room
www.urchin.com – Site stats analysis software which now owned by Google
www.webtrends.com – Another great traffic analysis software
adwords.google.com – Google service to purchase ads in their search engine
www.regnow.com – another affiliate marketing network
www.hey.lt – lithuanian counter
www.enigmasoftwaregroup.com – official site of American Company, creators of popular remover spyhunter.

and many more….
along with these sites our sites are blocked:
www.jurgita.com – online modeling magazine
www.2-spyware.com – antispyware community

All these sites are not malicious or posing any threat to the user. Blocking these sites can be harmful for the user. We tried to notify creators of this file and instead of that we got banned from their forum. here is the whole story with quotes: hpHOSTS – untrustworthy resource