Grails has been getting a lot of positive feedback so far – see some of the links to developer’s comments on Graeme Rocher’s site here.
From my own experience, it really has blown me away how quick it is to get an app up and running, at least through the prototype stages to get a functional app that people can look at. This goes a huge distance to helping people visualize the app and shape the requirements of what the app should do. It really has opened my eyes as to how much time we spend developing Java web applications messing with the ‘plumbing’, configuration and infrastructure parts of the application, before we even get to developing the part that counts, the actual functionality of the application itself.
I’m still working on a Online Store web application in Grails, and I’m hoping when I’m finished to have it hosted as an open source project so people can download it and take a look at a non-trivial application in Grails. The real benefit though is not in the implementation itself, but how fast and easy it was to get 80% of the application complete (I say 80%, because I’m finding now that I’m stuck refining the app to get it to do exactly as the customer wants, and it’s this last piece to polish it up that has actually taken the most time (but mostly because I’m not a HTML/CSS UI expert).