just leave your /etc/hosts file alone. it is a file owned by root and casual users should not need to fiddle around with it.
use firefox with adblock and the adblock-filter-updater for the ultimate browsing expirience

if you must, you can also install a proxy server (squid, see a fast guide here - http://mkeadle.org/index.php?p=14) or (if you are bored to hell) use linux build-in firewall to block unwanted connections to hosts.