Joel Spolsky has a very good argument included in his latest article, Language Wars, if you are considering trying Ruby on Rails.
Before you flame me, Ruby is a beautiful language and I'm sure you can have a lot of fun developing apps it in, and in fact if you want to do something non-mission-critical, I'm sure you'll have a lot of fun, but for Serious Business Stuff you really must recognize that there just isn't a lot of experience in the world building big mission critical web systems in Ruby on Rails, and I'm really not sure that you won't hit scaling problems, or problems interfacing with some old legacy thingamabob, or problems finding programmers who can understand the code, or whatnot. So while Ruby on Rails is the fun answer and yes I've heard of 37 Signals and they're making lovely Ruby on Rails apps, and making lots of money, but that's not a safe choice for at least another year or six.
He goes on to talk about something I have lived by for years. Write what you know, unless you are just trying to have fun.
It's good to explore and try new things. You may make major improvements to yourself, your code and your company. But don't gamble on critical systems. And if you have existing code, think very hard before you introduce new technology. It just compounds the learning curve.
Read Language Wars by Joel Spolsky. No really, read it.