I second that, specially if you're thinking about developing Web Services with Java, as data binding has been removed from the new JAX-RPC (JAX-WS).
J2EE vendors will need to provide or use a JAXB implementation to be compliant.
As a feedback we've been using JAXB 1.1 for over a year without problems. Our XML Schemas are somewhat complex and JAXB handles them nicely, something that WSDL2Java from both Apache Axis and IBM Websphere didn't.
Regards.