The disciplines of Information Architecture (IA) and Web Usability are converging. This is a good thing. The latter group is beginning to conclude that -- other UI stuff notwithstanding -- usability at its core has a lot to do with navigation and navigational expectations, which in turn revolve almost completely on taxonomy and metadata quality on large websites. IA specialists are realizing that usability people bring strong methodologies for testing categories and vocabularies in the environment where metadata plays out most importantly: on websites. Don't worry about the debates-by-blog between some in the Usability and IA camps. This is the natural byproduct of smart people concentrating intently on complex problems. Meanwhile, check out the 4th annual Information Architecture Summit, where you can learn a lot about both IA and Usability, this March in Portland, OR, USA...
Visit the IA Conference Website