I\'m starting a project using a Restful architecture implemented in Java (using the new JAX-RS standard)
We are planning to develop the GUI with a Flex application.
Actually were are already using Flex with a Rest-Style Framework. As mbrevort already mentioned PUT and DELETE methods cannot be directly used. Instead we are doing PUT via a POST and for DELETE we are using a GET on a resource with an URL parameter like ?action=delete.
This is not 100% Rest style, so I am not sure, if this works with a JSR 311 implementation. You will need some flexbility on the server side to workaround the PUT and DELETE restrictions.
With regards to error handling, we have implemented an error service. In case of an server side error, the Flex application can query this error service to get the actual error message. This is also much more flexible than just mapping HTTP return codes to static messages.
However thanks To ECMA scripting of Flex working with XML based REST services is very easy.