Omg, there's a Shake Shack in London since July 2013 and I only found out now! What a shame..
For those who have never heard of Shake Shack: they have the best burgers and the best fries EVER. They started out as a hot dog cart in Madison Square Park, NYC in 2001. In 2004 they opened a permanent kiosk in the same park and every day again there's a huge line.
I've been to the one in Madison Square park in 2012 and I can tell you: it was worth waiting.
Shake Shack London
24 Market Building, The Piazza
London, WC2E 8RD