Valve Software has started taking legal actions against cheating (cheat-sites, cheat creators). According to a post by Gabe Newell on the Half-Life 2 Fallout Forums.
We"ve started taking legal action against cheating (cheat-sites, cheat creators,...) both in the US and abroad. This is in addition to the on-going investments in anti-cheating technology. You"ll see reports of this percolating up as various actions happens.