I don't have much experience in bringing rails applications into production, but I've toyed around with rails and asp.net for the past year and a half or so, and here's my take on the 'learning curve:'
This wording is largely stolen from the book, 'The Rails Way', which I've been reading for the last couple nights, but...
Rails seems very 'opinionated.' The more facets of the framework that you learn about, the easier your life will be. In line with Ruby, Rails is quite flexible... you CAN just go for it and with the help of Activerecord, scaffolding and the routing system you'll have some reasonable functionality with almost no effort whatsoever. However, the correlation between using Rails idioms/design patterns and your productivity is very close. With a good book in hand (I strongly suggest 'The Rails Way' for long-term Rails knowledge. Perhaps something smaller and cheaper will suffice if you just want to make THIS application and make it fast.) and a newly developed habit of READING (The Ruby and Rails community have a vibrant selection of weblogs and articles ranging from best practices to simple how-to's.) you'll have no problems. In a sentence:
Learning to do things the 'Rails way' will take some time, but Rails is designed to get your application up and running with as little fuss as possible.