The interesting thing here is that Twitter hasn't even infringed by design. The celebrity culture is more a matter of who happened to find the service useful. If you can be sued for something you didn't even implement but is an artefact of how your platform is utilised by users, well, there's a problem.

What's next, suing Apple because consumers can stick an iPad to their fridge therefore infringing on 'System and method for affixing a touchscreen to a refrigeration device'?