I would like to have jumped right onto the Rails bandwagon if it hadn't been for the fact that ActiveRecord offers only a fraction of what Hibernate does.
- Where is the proper transaction & conversation support?
- Why is it that it hits the db orders of magnitude harder that Hibernate does and is infinitely slower?
- Where is the criteria support? What about distributed caching?
And I would probably have said a long goodbye to Java, if it wasn't for the fantastic innovation that is happening in projects like Spring and Hibernate and the libraries that integrate with them (Quartz, Sitemesh, Compass, Acegi, Webflow et al) which Grails is built on. Want an RMI, burlap, http, soap or DWR service? Just expose one. Need advanced declarative security at the web and business layer level? Plug it right in. Job scheduling? Job done. Search? Sure no problem.
Spring and all the projects that integrate with it, make the Java ecosystem a very happy place indeed. So no, Grails might not have RJS (yet), migrations (yet) or xyz feature from Rails, but it has plenty, thanks to the Java eco-system, to make up for it and then some.