There has been a lot of hype out in the development community over the past year regarding Ruby on Rails, even with Ruby alone. For those that are unaware, Ruby on Rails is a full stack web framework written in Ruby. While I've only read the first 100 pages of Agile Web Development with Rails, I can say that RoR is very intriguing. At a high level, RoR relies on a MVC architecture, using the ActiveRecord design pattern for data persistence. I've found radrails to be an excellent IDE for RoR if you're developing on a Windows machine. If you find that you really enjoy Ruby, but work in .NET, I'd suggest looking into RubyCLR created by John Lam.
Back to .NET, the Castle Project, where DynamicProxy lives (this is used in Rhino Mock to intercept mock interface calls); is also host to several other interesting projects relative to the .NET world. MonoRail is an attempt to provide much of the functionality seen in RoR within the .NET environment. I can't help but wonder if we will see something come from Microsoft in an attempt to fill this space with a commercial product similar to how they have provided a testing framework in VSTS and their ATLAS implementation that is soon to be released all of which were rooted in open source products.