Spotify replaced Twisted with Smisk for one of its backend services, which marks the first serious deployment of Smisk! Version 1.1 is soon to be released and will be announced on smisk-announce as well as in this blog.
Smisk boosted performance for some services in 10 multiples, when compared to Twisted.
Smisk is a high-performance web service framework, with its core components written in C, but controlled by Python. Smisk also exposes a MVC-inspired package, adding Transparent Content Negotiation, class tree routing, templating, ORM-support, etc. Read more at the Smisk website.