Don Box takes the position that Ruby is a competitor to Microsoft in this blog post: Gosling on Ruby. He goes on to comment that "Java will take its rightful place as the successor to COBOL"
Java still has legs. The reality is that it will be quite some time before I could sell a Ruby based product to our customers (top tier financial organizations). Why is that? Well, simply put, the IT folks in these environments have a lot of things to worry about, and proving out a platform is not something they would relish. Java is the devil you know, versus Ruby as the devil you don't.
Having said that, I think a lot of the love Ruby is getting these days is because of Rails (and therefore by extension the Active Record pattern). Maybe the real competitor to Microsoft is not the language per se, but a simpler platform for building out web apps than what .Net can offer. That leads me to wonder what the commercial implications of getting Ruby running on the CLR are, and why MS hasn't picked up the ball and run with it yet.
Ironically, I don't think RoR impacts the Java community, which has a history of embracing choice when it comes to web frameworks, in the same way. It certainly isn't a stretch to imagine that somebody isn't going to port RoR to Java pretty soon, or at least build the next web framework based on the ideas of convention over configurability. There has also been some good movement in supporting Ruby on the Java VM lately.
I've been meaning to check Ruby out - I'm interested in what the fuss is about, especially with the "continuation" idea. But you know, I keep hearing about the problems people are having, and deployment is a pain, and there is no IDE, and... Wait a minute, this reminds of that old joke: Hey Ruby, 1995 called and it wants its "hype around a new language" back.
Update 2006-05-07: Ted Neward has posted some interesting observations around this thread here.