EDIT: Please note this is from 2009.
In the guide on how to counter Evelyn, someone asked how to counter Warwick. This is EASY.
Warwick, played in an ideal situation, is an absolute BEAST. Left alone in the jungle, he will farm FASTER than your heroes in a dual lane (not quite as fast as a solo). This means that while your team gets 1 solo and 4 duals, his team gets 2 solos, 1 half/solo, and 2 duals. Not to mention that he will kill the dragon about once every 5 minutes, which is a free tower for their team. All in all, an enemy warwick benefits his entire team massively in gold and xp.
Also, an enemy warwick is 90% of the time unaccounted for by the other team if he's jungling. That means he can gank you easily, and with his ult that's a scary proposition with 2 other heroes focusing you down.
The good news? There's an easy way to totally nullify his impact, all game long. First let's examine what is important for him.
A jungling warwick's first item is almost invariably a Razor (chance for 500 dmg to creeps per hit). A well-built one can take a golem/lizard camp at level 1. While the guide for Warwick suggests lizards, I and many other good jungling warwicks take the golem first. The golem is Warwick's biggest asset in early jungling (pre-level 6). It lets him spam his spells to jungle both faster and safer. Thus, early on, the key to defeating warwick is to disrupt his jungling.
HOW TO COUNTER WARWICK.
1: Summoner spells. Clairvoyance and Boost.
Clairvoyance is Warwick's biggest foe. It provides u with info on his whereabouts when normally you would have none. Have 2 clairvoyance users on ur team, and with intelligent placement, you will always know roughly where he is. (Remember, make sure to ward the golems ASAP. Like, before the game starts). If you see warwick junglin? STOP what you are doing if it's just laning (other things may be more important), and -go disrupt him-. When he's low finishing off them golem, make him run. That'll reset the golems hp when he returns, and warwick will be nearly dead. He'll have to go heal: you've just thrown off his earlygame.
Midgame and later on, it becomes more important to ward the dragon than the golem (though still important to disrupt that when you can). The dragon is a huge boost for warwicks team: don't let him take it freely. Take it YOURSELVES if you can ever afford to do it. Knowledge is power vs warwick.
Boost. Warwicks ult is less than useless when the enemy player has boost: It turns into a SELF stun. Warwick disables both himself and an enemy for 2 secs with his ult. A timely boost out of it will let u start pounding on him as he slices at air.
Now that you have summoner spells down, we've mostly talked already about this second one.
2: Teamwork. Disruption. Using your knowledge from clairvoyance, don't let warwick sit around and farm. Ever let a tristana sit in a lane for the first 15-20 minutes and just freefarm? Remember how that game ended? Warwick may not be the insane carry that trist and ashe are, but he's pretty good when farmed. Don't let him be. Throw off his game plan. Gank him, especially if hes jungling.
One last little incentive to kill warwick: he loves to get neutral buffs. They transfer to you when you kill him. Allow your mana-hungry or ranged dps heroes to get the golem/lizard buffs respectively, and listen to the other team yell at Warwick for granting you free glyphs.
I feel like I'm repeating myself so I'll stop here. Feel free to ask any questions