First I've read some about Groovy, and it's really easy the syntax and I like it.
Then, I've read about Grails architecture and the User Guide.
My impresion it's Grails is not much diferent than Appfuse, step by step:
- GORM and Domain Model, is based in JPA and Hibernate. (domain centric approach explained by icoloma)
- Controllers are based in Spring MVC.
- IoC with Spring (of course).
- Layouts based in Sitemesh.
- Also you have Web Flow with Spring Web Flow.
- Both are a simple WAR file.
Graeme Rocher gave a kick ass to someone that say no :D. I think it's ready, you have to take care about your code like in any other language.
The only thing I miss, is better support for Groovy and GSP in Eclipse (autocompletion, refactor) and manage the dependencies.
update: Guillaume Laforge thoughts about Enterprise Ready