[wheels]

I'll put forward a more blunt answer: because Rubinius is the only tenable way forward, long-term, for Ruby.

MRI is a steaming pile. (Note: You're not allowed to disagree with this unless you're a C programmer that's spent some quality time with MRI's code.) It seriously shook my faith in Ruby the first time I had to dive into MRI's code: "Could someone who waxes poetic about elegance and fun in coding really produce something this fugly? Does Matz have any idea what he's talking about?" Rubinius has a sane design and is a pretty clean base to build a Ruby implementation with some staying power on. I basically see Rubinius as the rewrite that MRI was going to have to have at some point.

That said, at present, I still use MRI. I try Rubinius every couple months to see how it's progressed performance-wise for the cases that I care about, and while it's not there yet, this seems to be mostly a matter of time.

[jshen]

I'm all jruby all the time these days, and I couldn't be happier.

[steveklabnik]

How do you feel about YARV? I mean, Matz has always been honest that he's not a compiler guy...

That said, I think rbx is the way forward too.

[riffraff]

my hopes for the future are in RBX but why would the ugliness of MRI (I assume you include yarv in it) make it untenable in the long term?

There is a massive amount of bad code on the intertubes that has been around for decades, and I kind of hope we will not be programming in ruby when it's 40 years old.