Yes, Ruby is ready for the Enterprise
David Heinemeier Hansson quite rightly critiques James McGovern's anti Enterprise Ruby article.
To say that Ruby and Rails are not for the Enterprise is like saying that PHP, Perl, Common Lisp, Smalltalk, etc. are not ready for the Enterprise. What ever happened to thinking about using the right tool for each job? Factors influencing "what is the right tool?" decision certainly include:
Existing knowledge and experience in your organization
Runtime efficiency and reliability
Time required for Development
Effects on maintenance costs
Existing software libraries and infrastructure software
etc.
Don't get me wrong: I love server side Java for solving many different types of problems, but lighter weight (often scripting) languages and platforms also have their uses and there are many types of problems that are better solved with Rails than some subset of J2EE.