What methodologies do user experience professionals adopt that differentiate them from usability professionals.
Many others have attempted to define the roles within user experience, but there are no hard boundaries.
Jesse James Garret descibes in his book The elements of User Experience (See overview) includes Usability as part of the Strategy Plane, although I'm sure he would agree that as in so many situations, the components of user experience do not fit neatly into little standalone boxes, but spill out into other areas. [Note that JJG adapted his top level 'element' from Visual Design to Sensory Design]
So, I think the Bible (That's Information Architecture for the World Wide Web by Peter Morville and Louis Rosenfield) very nicely describes various roles within the industry:
I quote directly from Chapter1 of the book: (which I heartily recommend in order to find out about the various methodologies you ask for, as I feel that is too wide a topic to answer here)
Gray areas and caveats aside, here is our attempt to draw some boundaries between information architecture and a number of closely related disciplines.
Traditionally, a graphic designer was responsible for all aspects of visual communication, from the design of corporate logos and identities to the layout of individual pages. On the Web, we’re seeing increasing specialization due to the complexity of the environment. Even so, many graphic designers do a great deal of information architecture as part of their work.
Interaction designers are concerned with the behavior of tasks and processes that users encounter in software and information systems at the interface level. They often have a background in human-computer interaction, and are focused on helping users successfully achieve goals and complete tasks.
Usability engineers understand how to apply the rigors of the scientific method to user research, testing, and analysis. Their background in human-computer interaction and their experience observing users provide them with useful insights into design. They are often concerned with testing all aspects of the user experience, inclusive of information architecture and graphic design.
Experience design is an umbrella term that encompasses information architecture, usability engineering, graphic design, and interaction design as components of the holistic user experience. You’ll find relatively few “experience designers,” as there aren’t many people on the planet with skills in all these areas. The term is useful insofar as it encourages cross-disciplinary awareness and collaboration.
People rarely confuse software development and information architecture, but the two fields are highly interdependent. Information architects rely on developers to bring our ideas to fruition. Developers help us understand what is and isn’t possible. And as the Web continues to blur the distinction between software applications and information systems, these collaborations will become even more important.
Content management and information architecture are really two sides of the same coin. IA portrays a “snapshot” or spatial view of an information system, while CM describes a temporal view by showing how information should flow into, around, and out of that same system over time. Content managers deal with issues of content ownership and the integration of policies, processes, and technologies to support a dynamic publishing environment.
Knowledge managers develop tools, policies, and incentives to encourage people to share what they know. Creating a collaborative knowledge environment means tackling tough issues surrounding corporate culture such as “information hoarding” and “not-invented-here syndrome.” Information architects focus more on making accessible what has already been captured.
i look at usability as part of user experience design, an integral part of it. the different aspects of user experience design are so interconnected that usability just cannot be a standalone something
your user interface design with usability considerations will contribute to user experience, your copywriting will contribute to overall usability, and testing all of this will help find issues.