A Harro principal, Mr. Andrew Peters recently spoke at Ad:tech. The subject was about virtual worlds and in particular, the Twinity virtual world. Even after the slight setback at SecondLife, investments into virtual worlds continue to climb, and the eventuality of Virtual World becoming mainstream media is becoming a reality.
So what should you be looking out for? Typically the size of the communities in the various worlds, and the top in-world destinations.
From a technology point of view, the ability to integrate off-world media with the platform is important. This is one of the key aspects of Twinity.