Rails 4.0.1 has been released
weblog.rubyonrails.org
weblog.rubyonrails.org
http://weblog.rubyonrails.org/2013/6/25/Rails-4-0-final/
I'm very impressed with Rails 4, not just the overall level of improvements, but also the stability of what was released. To go more than 4 months without a patch is especially impressive for something like Rails."Agile Web Development with Rails" also does CI against edge edge Rails, so that's being checked at all times too.
I'm not going to say there's a ton of production apps using latest, but there are some, at least.
http://www.techempower.com/benchmarks/#section=data-r7&hw=i7...
For workloads that require super high performance, one can simply use something else... Java, Node.js or whatever. Now that Phusion Passenger supports Node.js as well, it's very easy to write some parts of an app in Rails, and write other (performance-critical parts) of an app on Node.js, and deploy them together on a single server with ease.
The problem with Node is, you have to load up a runtime. That can not only kill your performance gains, but actually make things slower.
Specifically, try using the apr (apache portable runtime), or leverage tomcat (which can use apr) + jruby + jndi jdbc connection pools.
Let rails be rails, your best bet for performance is either making the underlying ruby runtime better or leveraging things that are designed to be high performance.
Round 6 didn't have this many errors
http://www.techempower.com/benchmarks/#section=data-r6&hw=i7...
Do you know off the top of your head if reorder will behave as order does in 4.0.0 (including nested scopes and associations)?
[Edit: It doesn't look like reorder does the job as it just drops existing orderings so you can't have a sequence of such calls. Don't think I like the reversion better to fix the API and the applications at migration to Rails 4 rather than persist the mistake.]
Flask is a microframework that often fits within one file and is probably more comparable to Sinatra than Rails. I've only ever used it for setting up really small webservices and stubbing webservices. It could certainly scale up to larger apps, but it doesn't give you a lot of direction in how best to do so.
Rails is a full-stack framework. Out of the box it gives you everything from the view to the database and strong conventions for where to place classes as your app grows. In general, it's more often compared to Django.
[1] http://learn-rails.com/learn-ruby-on-rails.html
[2] http://ruby.railstutorial.org/ruby-on-rails-tutorial-book
[4] http://pragprog.com/book/rails4/agile-web-development-with-r...
ALso, http://pineapple.io