The trains will run along the Jubilee line up to and during the Diamond Jubilee weekend. The first wrapped train went into service on Monday 14 May 2012 and the second will be from 21st May.
TfL have pointed out that the decorative wraps have been funded by Tube Lines "at no cost to the tax payer".
You've probably also spotted a number of posters around the system advising us to check TfL's website for any special travel arrangements over the Jubilee weekend. My favourite is one with a pair of corgis looking into a laptop. There's also images where only a guardsman's bearskin and the Queen's crown can be seen over the top of the "royal" laptop.