Spring 3.0.1 has solid JAX-WS web services support. At the same time, I see that many articles refer to Apache CXF as a great web services framework.
If I work in the Spring/Hibernate world and want to expose the high-performing web services to the front end, should I consider utilizing Apache CXF? Is there any advantage to adding this additional framework to the mix?
The two are not mutually exclusive. Apache CXF is fully JAX-WS compliant.
Remember, JAX-WS is just a specification. Spring talks ato that spec'd API, and doesn't much care which implementation you use. Java6 ships with an internal JAX-WS implementation (Metro, or part of it), and CXF is merely an alternative implementation.
CXF is probably a bit more capable than the JAX-WS that ships with Java6, but unless there's something specific that you need that Java6 doesn't provide, I'm not sure it's worth the bother.
As for Spring and JAX-WS, Spring just makes it a little bit easier to use.