Although I just got to delve into it for a short time, but I can't wait to use it in my real java projects. And it's proved to be success application in real projects, such as Groovy Templates (SimpleTemplateEngine), it's definitely superior compared with JSP. My java projects look much clean now for the email content/report generating and dynamic web widget generating.
To a Java developer, it's definitely amazing language. I like a language that without a lot of surprise to learn. Everything in groovy is just so nature and elegant. If you learn ruby, for a Java developer, you will see a lot of surprise which you have to remember. But in groovy, you don't need to remember much things, what you want is what it designed like.
Hope Sun can provide more support in their IDE (NetBeans) instead of diverting too much effort to a totally different script language such as JRuby or create some new language such JavaFX. I believe it's the future of the Java. Itís not just a toy which only can be used to write testing or do some prototyping. I hope to see Java language designers can incorporate some of the nice concepts into java language itself in the future versions. Such as string literal, closures, they are not necessary only be available in scripting language. It's just short cuts in the source code level, but definitely will make your code much clean and elegant. And make you work more interesting because you are more concentrate on the problem you are solving, instead of having to type a lot overhead syntax just to make compiler happy but makes your code more polluted.