Based on a recent court decision in Europe, maybe not as much as you might think. First, a trademark includes any word, name, symbol, or device, or any combination thereof … to identify and distinguish goods … (US Trademark Act of 1946).
On August 4th, Google said it will let European advertisers buy search-ad terms – even if the trademark is owned by another entity. Sounds wrong? Well, a European court ruled in March that just such an action freed Google from liability.
This ruling just might be a bonanza for counterfeiters/knock-offs at the expense of the rightful owner of the trademark. My hunch is, at least in Europe, the value of trademarks (in general) just decreased.