Blizzard introduced advertising on the Official WoW forums. So far it looks like mainly WoW tie-in products. I don't really have an opinion, other than the ad on the right is a bit annoying because it wastes a lot of space.
But the ads have spawned the thread Rise Up, Sons of the Horde!, which is legendary. Here are some choice samples:
Foolishly you have sought your own bankruptcies. Brazenly you have disregarded offers beyond your understanding. You have browsed hard to invade the realm of the t-shirts and minis. Now there is only one way out — to walk the lonely path of the checkout line.
The Mengarie is for paying customers only.
RECESSION HERALDS THE END OF YOUR WORLD. COME, MORTALS! FACE THE WRATH OF THE PRICECHOPPER!
Stop clicking me! Me not that kind of ad!
Sales, Bargains. My people are addicted to it... a sale made manifest after the Sunwell went out of business. Welcome to the future. A pity you are too poor to buy all this. No one can stop my T-Shirt bonanza now! SELAMA ASHAL"ANORE!
You landlubbers are tougher than I thought! I'll have to upgrade online to WotLK!
All department stores, all outlet malls, are open to me!
Bargains have brought you here to me. I shall be your salesman.
Simple shoppers, credit is the fire in which you'll burn!
Ragnaros: TOO SOON! YOU HAVE SOLD OUT TOO SOON, EXECUTUS! WHAT IS THE MEANING OF THIS CLEARANCE SALE?
Majordomo Executus: These mortal customers, my lord! They have invaded your store, and seek to purchase your merchandise!
Ragnaros: FOOL! YOU ALLOWED THESE INSECTS TO RUN RAMPANT THROUGH THE HALLOWED STORE, AND NOW YOU LEAD THEM TO MY VERY CASH REGISTER? YOU HAVE FAILED ME, EXECUTUS! BARGAIN PRICES SHALL BE MET, INDEED!
Ragnaros: NOW FOR YOU, INSECTS. BOLDLY YOU SOUGHT TO PURCHASE THE MINIATURES OF RAGNAROS! NOW YOU SHALL SEE THEM FIRSTHAND!
C'thun whispers: Your friends will abandon you for hot bargains.