Virtual Worlds are the new frontier (and a bit of a favoured subject of mine), they are very much an unknown quantity when it comes to the law and in particular protecting intellectual property rights.
By "Virtual Worlds" I am referring to Massive Multiplayer Online Role Playing Games or MMORPG's for short. In these games the user takes control of a character and guides them round an online world. There are different types of MMORPG's some are more 'game' orientated with specific tasks to complete and rewards given for completing these tasks (for example World of Warcraft) and some are 'simulation' types for example Second Life, in which you control your character in a more realistic world where you do everyday tasks such as getting a job etc.
The interesting aspect in these Virtual Worlds (in a legal sense at least) is that many of them allow user generated content. Take the following situation for example: on Second Life a user can create content, what happens if a user makes a pair of Nike trainers for his character, is this a trade mark infringement? (probably not because it would not be in the course of trade) but what happens if he then decides to sell these trainers to other users, this would surely be an infringement of the Nike trade mark. In such cases the virtual world themselves would be liable as in a lot of cases the worlds retain ownership of intellectual property see for example World of Warcraft etc but Second Life is leading the way in allowing content creators to own the intellectual property for the content they generate, thus this transfers any legal issues to them also.