I just recently been using the host file for an extra layer of protection and what it does is blocks ads, banners, 3rd party Cookies, 3rd party page counters, web bugs, and even most hijackers and some block malware before your even able to access the website.
Some premade ones can be found here:
MVPS: http://winhelp2002.mvps.org/hosts.htm
HP: http://www.hosts-file.net/
HostFile: http://hostsfile.mine.nu/
There are tools to Modify host files like:
HostsXpert: http://funkytoad.com/index.php?option=com_content&id=13
Host Man: http://www.abelhadigital.com/hostsman
Warning: Some Legits Websites Can Be Blocked By The 3 Premade Ones Above
But you can always restore the Default one easily.
More Info On The Host File Can Be Found Here: http://accs-net.com/hosts/what_is_hosts.html

