It's still a work in progress and at the moment has only the stations he knows well: King's Cross, Old Street, Bank/Monument, Oxford Circus, Seven Sisters, Walthamstow Central and Shadwell & West Silverton on the DLR. Hat tip to James Whateley for alerting me to this.
You can drag each view to spin it, and use the mouse wheel to zoom the view. You can focus on different parts of the model using the "Focus:" selector, and hover over features to get information.
There's a lot of discussion on a discussion group for things you'd like to see added, corrections, improvements etc which Andrew seems to be taking on board.