The key with 1.9.3 is it's essentially work on producing a better implementation internally. The language is mostly unchanged since 1.9.2 but 1.9.3 is a lot faster in specific situations. Couple this with the newly customizable GC settings (I'll be blogging about this shortly) and 1.9.3 is shaping up to be a fine release. 37signals are already using it in production, even.
Scroll down on that page for some more lengthy explanation.