I'm learning Rails right now and this isn't the first time I heard how slow RoR can be. Hell, there's a whole site answering the "Can rails scale?" question (http://canrailsscale.com/).

A lot of what Rails does, and even the little things, like naming conventions in ActiveRecord, intuitively make sense to me. If RoR ever does expire because another language/framework displaces it (maybe Elixir/Phoenix?) or because of poor/no support from a big company, I wouldn't look at it as a waste of time. Overall, I'm seeing a tried-and-true method of creating web applications and I'm enjoying it so far.

RoR can still get you where you need to go and fast, which is what you need when starting out. And if you ever find yourself in the same situation as Twitter, then you can make the switch...or better yet, improve on Ruby and give back to the Ruby community.