Everything looked great but during project setup, I selected the option to use Warbler ('Add Rake Targets to Support App Server Deployment (.war)'). As it turns out, setting up Warbler during project setup just 'breaks'. I have been using the "Built-in JRuby 1.4.0". It seems to be a path issue on my Mac running Snow Leopard (there were some indications on the web).
Ultimately, I was able to solve that issue by installing a dedicated JRuby version that had a nice shorter path.
"/Applications/NetBeans/NetBeans 6.8 RC2.app/Contents/Resources/NetBeans/ruby2/jruby-1.4.0/bin/jruby" -S gem unpack warbler
Command failed with status (127): ["/Applications/NetBeans/NetBeans 6.8 RC2.a...]
/Applications/NetBeans/NetBeans 6.8 RC2.app/Contents/Resources/NetBeans/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:995:in `sh'
(See full trace by running task with --trace)
/Users/hillert/_APPS/jruby-1.4.0/bin/jruby -S gem unpack warbler
Unpacked gem: '/Users/hillert/NetBeansProjects/DX2010/vendor/plugins/warbler-0.9.14'
I haven been running into a few other issues to finally get a simple Rails deployment working on my Tomcat instance, but that is a new blog post to come...