Is Rails 2.3 a first step towards Rails 3.0...?

a new version of rails is always a step ahead. of course you can
profit of any knowledge you gain on rails 2.3 since the most of it
will still be true in rails 3. there will be new things in 3 and there
will be some deprecated things, but basically it's still rails and not
merb or anything else. don't worry too much. just keep on learning and
coding...