I'm also developing an open source RCP application whose architecture is
very similar to what Filippo describes.
A server component, spring-based, runs with Tomcat. I'm also looking at
Spring Dynamic modules as replacment, but
as far as i know, HTTP remoting is not yet implemented.
This server component manages model object persistence (same
service->dao->Hibernate pattern ) and exposes through HTTP remoting a set
of "services".
The client RCP application includes spring framework core libraries and
uses HttpInvoker to communicate with the server.
Acegi is also used for, currently very basic, basic security.
Services provides by the server allow RCP client to fetch some objects,
create new ones or run specific process.