IMO if you build a product and it is working, there really is not much reason to redo your efforts in a higher performance framework unless your needs require you to do so. If you are at your current hardware's limits and you can't throw more hardware at it (for whatever reason), it may make sense in that case. If you want to reduce the amount of servers you currently have, it also makes sense there. http://blog.iron.io/2013/03/how-we-went-from-30-servers-to-2... This is a great post talking about going from 30 servers using Ruby to 2 servers using Go.

Use case example - Twitter was using Rails on the front-end for a while but it got to the point where using it made little sense. Part of Rails' performance is dependent on caching - which is really hard, if not impossible, to do well when you are dealing with live data.

FYI, Gemini is our framework that we've built and maintain internally. You probably won't find reference to it (except for out blog).

edit This is the link to Twitter's blog about Rails http://engineering.twitter.com/2011/04/twitter-search-is-now...