Hi Bart,
Our organisation has been very active in Second Life for the past 7 months, and I agree with you 100%... it is worth having a presence in-world. Not only for the media potential, but also because of the direction of internet technology development globally. The prediction that 80% of current users will be in a virtual world within 5 years time, is not far-fetched and if you take into consideration that more than 150 universities are currently present on the platform, the collaboration benefits alone exceed the marketing benefits. Be an early-adopted to lead and shape thinking of the youth. More to loose NOT to be part of this amazing opportunity I would say!
I further agree very much with the comment that social networking sites are critical for viral marketing of causes such as your own. However, for me...it is a combined between traditional ways, social networks and virtual worlds that holds the key! It is not an either or scenario... I would also not list 'numbers' as the greatest strength of web platforms such as SL - but rather the immersive, creative environment and opportunity for free expression and collaboration with innovators!
Find us in Second Life - we are the first African-based civil society organisation there! Uthango Social Investments
http://slafrica.wordpress.com