Can we say that Usability, User centered design,
Information Architecture and interaction design fall under the umbrella
of User experience design?
I think Dan's Diagram  shows this well.
@Josh - You are right the diagram of KICKER STUDIO is one of several good interpretation / illustration
At this point of “present” I think of the UX honeycomb of Peter Morville  …
honeycomb – Peter Morville (P.Morville – Facets of the User Experience)
Or my own one ...
UXD-P – Gathering the elements
The diagram below presents the relationship of the elements above (
Elements of UXD-P
And you should always have a look at the one of J.J. Garrett:
Source: "The Elements of User Experience." Jesse James Garret. (PDF)