The Java Code Geeks has a blog post on using the RESTEasy REST framework with Spring-based services. While I would recommend the Spring REST support in Spring MVC over this approach, it's at least interesting to have the recipe if you ever need to use it.
The Java Code Geeks blog has another post on building Spring-based JPA services that sit behind a RESTful CXF backend. This is another one of those situations where, while it's useful to know how to do in case you need to, you're better off using Spring MVC's REST support. It's easier, and integrates more naturally with the component model.
The Banging My Head Against a Wall blog has a great post on Upgrading from Spring 2.5 to 3.1.
This blog shows that the migration is dead simple, if you haven't already made the jump, and he's got insight into one particular little gotcha you might hit to make the migration that much smoother.