This question was raised and discussed at stackoverflow recently. Having used Grails for the sixbee project I shared our experiences compared to standard J2EE application development, especially to the subquestion:

Does it really confer rapid development benefits?

Definitely, it does. Even if the scaffolding path is left early and conventions are overriden to the own needs, the start-up period is very short, as we don’t have to care for many different technologies. That kind of lightweightness makes us work not only faster, but also more precise and clean. >> more…