Andrès reports: "Office Depot has sued its rival Staples over their misuse of the Adwords in Google. Office Depot has an online subsidiary for office supplies called Viking Office Supplies. Staples paid Google to redirect customers to their site if they looked for 'Viking'."
Well, I am not sure Staples paid Google to redirect customers. They are only invited to click on an ad. When a person goes to a mall, she sees many trademarks displayed next to each other. There may also be ads in the mall itself (sounds, flyers, etc.). Let's assume that some of these ads are for the competitor of a shop which is in the mall - and this competitor has a shop in the mall: There would not be any lawsuit!