Hi Leandro,
I can't speak for everyone, but I know that I've introduced Grails into Government environments in Australia.
Whilst I can understand that conservative environments are naturally resistant to "newer" frameworks and products like Grails, there are still some fantastic opportunities to gain traction.
For example, I threw together two Grails applications in a day that have been in the "we need these apps but don't have the budget to spend a month developing them" category. I hear a lot of stories from other folks like this. Grails is really gaining traction in the "quick inhouse" app department, which I think will be the beach-head for bigger deployments in the longer-term.
I think one of the biggest Grails sites I know of is Sky UK. Million+ hits a day. Graeme has the details on his blog:
Sky.com relaunches written in Grails.
Glen.