I've been testing out Unity 3D ... with the goal of creating a light virtual world application. I've been using the SmartFox .NET/Unity API .. and it's been working great!! I have no prior networking type experience .. but I had a multiplayer game up and running in less than 24 hours.
The only concern I had was the server side and being able to scale depending on traffic and space.
Then I learned of Amazon EC2 (Elastic Compute Cloud) and it has been heaven sent ... I can now deploy Smart fox on EC2 and scale up or down dynamically at a lower cost than if I was using a dedicated server provider.
If you haven't heard of Amazon EC2 .. check it out here http://aws.amazon.com/ec2/
Also check out Smart Fox http://www.smartfoxserver.com/