Being the one widely supported client-side language for the web means that lots more money has been poured into making JavaScript implementations effective than has gone into Ruby (I wouldn't be surprised if Google put more resources into V8 than have gone into all Ruby implementations combined.)
True, but since V8 is open-source, shouldn't it now be possible for the Ruby developers to borrow the techniques from it that made Javascript so much faster?
None of the techniques that's gone into V8 are all that novel. Most of them - at least the ones that are relevant to Ruby - stems from research around Smalltalk and Self that's been well known for a very long time. The hard/time consuming part is implementing them.
Ruby isn't JavaScript. Studying V8's solutions to particular problems with making JavaScript efficient may help people seeking to make an efficient Ruby implementation, but how much is easily transferrable I don't know.
No doubt V8 is much more mature than MRI, I think some language considerations do still apply though, JavaScript doesn't have method_missing, problem #5 doesn't apply, I guess there is more.
