Which version of rails should I use?

I'm looking to build a web interface for an existing Ruby app and I'm
trying to figure out which version of Rails to use - 2.3 or 3.0.

The reasons for using 2.3 are pretty straightforward: it's stable and
I can buy a number of books on it.

My reasons for considering 3.0 are:
- My app uses Ruby 1.9 and Rails 2.3 does not seem to support Ruby 1.9
- From what I've read, Rails 3.0 is a major rework of the framework.
If I'm starting a new project now I figure I may as well do it 'right'
the first time rather than have to migrate it when I'm ready to move
to Rails 3.0.

Is 3.0's feature set really so much better? Is it stable enough for
use or am I only asking for trouble? Is it much more difficult to
learn than 2.3?

If you can run Ruby 1.9.2 then use Rails 3 RC1

otherwise stick to Ruby 1.8.7 and Rails 2.3.8