Please tell me that this is just a fascia though and that there isn't actually a Tube line that you can travel on? Or is it something that could potentially develop if people wanted to "build" one? Who would own it and would you have to pay to travel on it? I'm assuming there's a currency in Second Life, but are there virtual Oystercards? Personally I can't think of anything worse than travelling on a virtual underground. The real one is bad enough, so why would you want to put yourself through this in a virtual world?
Speaking of simulated Tube experiences, Londonist have posted a great video by Ben Cowell, from a band called The Schla La La's with animated Lego characters getting on the Tube at the beginning, giving each other some high fives
and then break dancing on the platform before the train pulls in.