Rails is Ghetto
I have to admit – while Rails is about 100,000 times better than the other alternatives (if, by alternatives, you mean “not so obscure that you’re up against astronauts in the odds of finding a job”) it is definitely one of the hardest things I’ve dealt with in a production environment and might have a few innate flaws that make that not just a “new kid on the block” issue. Scaling at ActiveRain was (and, from the Rackspace calls I still get, still is) a huge pain in the ass. And ActiveRain is small potatoes (well, possibly a medium).
Merb looks promising but, good luck selling that shit to clients, or, worse, hiring someone to help you out when you grow. I’m still going to learn it, it’ll be the shit in a year.