I was an Eclipse user before I started using Grails. It was quickly apparent that wasn't going to cut it. So I tried Intellij and NetBeans. At the time Intellij was better as far as Groovy and Grails were concerned. However, NetBeans was free and that made it good enough for me. Since then all three have had new versions or new plugins released. I am still using NetBeans because of the cost of Intellij. With the acquisition of G2One by Spring Source one of the expectations is more support for Groovy and Grails in Eclipse. This will be necessary for increased adoption.
Using Grails for a new project is wonderful. So much of the Enterprise Java baggage is no longer necessary. I can imagine trying to port something would be difficult because until you understand where a framework strength's and weaknesses are it is hard to utilize it efficiently. It is promised that JSP support will come easier in Grails 1.1, I don't know if using a beta version while trying to grok a new framework is a good idea. The testing has also gone through a major revision for the new version. If time allows you may consider waiting as the 1.1 release should be very soon.
If you have an opportunity to give Grails a try in a different IDE when starting a project from scratch I think you will see it in a different light.
