We launched GoNevis today, officially. (It's been on staging & production servers for a while but we announced it today.)
So far it seems to be running good.
GoNevis backend wouldn't be possible to implement so fast without using Python. We're using Django web framework and tons of other libraries including Celery and Django Rest Framework.
The decision behind choosing Python was basically due to our team familiarity withing the language and of course the nature of Python that gives us a lot of flexibility in terms of rapid development, no doubt Python is getting crazy popular every day and we're seeing new projects released by the open source community.