I'll ask Graeme Rocher about it this weekend at the Groovy/Grails Experience. He's the leader of the Grails project.
As nice as GORM is, remember that there is a lot that we owe to being in a container -- Hibernate, Spring, etc. are all there and optimized to work together in a fairly constrained way. All of the magical GORM methods get dynamically added by virtue of the directory that the POGO is in, and so on. Taking any old POGO and making the persistence magic on it could potentially be a wee bit more problematic.
I'm not saying it's not a good idea, and I'm not saying that it wouldn't be awesome. I just think that GORM outside of a well defined container might be more problematic than what you see at first glance...
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com