There's a couple errors or oddities in the slides.

Gerald Bauer wrote:
>   * Hash Keys Now Unordered

As someone else noted, hash keys have never been ordered in 1.8.6 or 
earlier. The example shown is in alphabetical order purely by chance. 
1.9 adds insertion ordering. JRuby also has insertion-ordered hashes 
already.

>   * Inject Methods

This is really a larger change, the addition of to_proc to Symbol 
similar to what ActiveSupport provides. It's not specific to inject.

>   * Decimal Is Still Not The Default

I doubt Decimal will ever be the default, no matter how people wish it.

>   * Break Values

This is no different than Ruby 1.8.x.

>   * "Nested" Methods

This is nothing new; a method defined in another method just defines on 
the same class, as normal. They're not really "nested".

There's also a "Real threading" slide that confused me. Ruby 1.9 does 
use real kernel threads, but they don't run in parallel.

- Charlie