Many online entrepreneurs do not realize that they may be held legally liable for keywords they select during their marketing campaigns, especially if they correspond to registered or famous trade marks. The present contribution highlights some of the most important aspects of the Google and eBay cases that illustrate this problem. The European Court of Justice has recently ruled that a search engine provider is not infringing trade marks as it does not "use" them in a legal sense. The advertiser, in turn, will usually be held primarily liable, although eBay dispute demonstrates there may be a room for manoeuvre for larger intermediaries. These legal developments are important, firstly because they promise to offer a greater protection to Web 2.0 business models based on user-generated content. Secondly, online business offering paid search services will be shielded from liability for storing infringing content provided that their activities remain technically neutral.