Nice comment. I really believe strongly that the fast iterations that python allows for is why companies are so successful. The argument that language x does not scale is a bit naive to the fact that they got to the point where they have enough users to make scaling an issue. Go is wonderful and I love programming in Go, but I would choose either python or node for web apps that require fast iteration. I believe that when offering services over the cloud, utilizing multiple languages for well built individual components is a great approach.
Much more along the lines of:
* Start with Python
* Have a great time and build successful apps with it
* Become global-scale infrastructure provider
* Hit problems that only occur at that scale and switch tools
The take-away is, you're almost certainly not going to end up at the size of Dropbox. If you're spending ages as a startup futzing around using bleeding-edge technology just because it's cool, you might well be wasting time – or at least prematurely optimising.
This is the perfect example – Dropbox has the engineering talent to write a set of libraries to implement basic features. Earlier-stage companies don't have that luxury.