Don't know if you've seen this, but it's brilliant.

This is advertising!

At Liverpool Street Station in London, T-Mobile "Life's For Sharing" did this great commercial unbeknownst to the daily commuters.  They practised for 8 weeks and also at 2 am the morning before at the station.  On January 15th, 2009, at 11:00 am, with hidden cameras and 400 dancers, their plan was put into action.
 
Enjoy!

http://www.youtube.com/watch?v=VQ3d3KigPQM