While Ruby 1.9 will have some nice advantages, such as speed, it has some huge disadvantages. Well, at least for the time being.

First off, Ruby 1.9 has some core changes to syntax. This is not a huge issue and can be overcome, however. It will make updating your current applications to be Ruby 1.9 compatible a headache.

Second, Ruby 1.9 does not have extensive Gem support. Reason for this is no doubt due to downside one. But, this will only be an issue in the beginning. As Gems update their code to work wtih 1.9 and new Gems are released solely for 1.9, then this will not be an issue any longer.

Third, potential bugs in the core? I am not sure if this would be an issue or not, but since they changed how the core code works and operates then one can expect there to be some bug issues with the new changes.

For me I can make the switch to Ruby 1.9 with no major issues. Why? Well, I do not have any huge applications running Ruby 1.8.x right now, however. I will still need to use 1.8.x on my machine soley because of Ruby on Rails.

As I am aware of, Ruby on Rails is supposed to be compatible with 1.9 when it came out, but I am leary to make the switch just yet. Reason being, Ruby 1.9 will surely have the above disadvantages when it is first released, and even if Ruby 1.9 did not have any major bug issues that does not mean Ruby on Rails will not have any bug issues with compatibility.

I believe I will wait a couple months before making the switch to Ruby 1.9. Maybe on the first or second patch update and once some Gems have updated their compatibility with Ruby 1.9 I will make the move to Ruby 1.9.