To add a little colour to your engineering comments: Facebook actually are in the process of building up a substantial engineering team in London, and they move

To add a little colour to your engineering comments: Facebook actually are in the process of building up a substantial engineering team in London, and they moved into new offices about 4-5 months ago to facilitate that. Google's been expanding their London engineering teams for some time now - both companies have a pretty significant focus on mobile. From my perspective (I work for a Valley based company, but head up the London engineering team) I see lots of large players and established start-ups creating engineering centers outside of the valley. I think there comes a point as a start-up where the benefits of scaling up your local engineering are outweighed by the advantages of opening up new global locations, especially when you're globalising your product..