Why did you choose to become an Information Architect?

I've never billed myself as an information architect. It actually isn't clear to me that labour should be divided such that there is a discrete role of information architect. The abstract skill set of information architecture crosscuts just about every domain of conventional expertise.

But then, I'm probably not normal: I design information infrastructure end to end, which ranges from sculpting organizational policy to writing the code that implements it.

What is information architecture?
That is an open debate. Morville and Rosenfeld hold it as the design of shared information spaces, or something to that effect. I submit that since information architecture uses information as raw material, it is virtually devoid of any content of its own. As such it is best demonstrated through copious examples.
What do you create for clients?
Ideally, I create situational awareness and conceptual integrity. Artifacts emerge as byproducts (and ultimately receipts) of that process—whatever it takes to achieve the desired state. Enough of the time I'm inventing them as I go along—there is no predetermined repertoire. I believe this concept is essential to understand. A persona, content inventory or wireframe is meaningless if everybody involved doesn't both understand and value it. The process of acquiring such an artifact is arguably more important than the artifact itself.
How do you evaluate or design a site?

Recently I have been exploring the clustering or partitioning of directed graphs, i.e., the fundamental structure of websites. This produces a natural hierarchical decomposition along lines which are not likely to be obvious to a conscious designer.

I've also been interested in forensics on existing sites. When a site is already up, we can state ipso facto that the author of a given page thought whatever is on it was important enough to publish. Likewise, the paths people take through a site indicate clusters of information that could be rearranged for quicker uptake.

One of the most significant properties of hypertext is that it is uniquely amenable to the composition of conceptual structures which are considerably more complex than what one can achieve with a book. This capacity for complexity can be applied in ways as diverse as exploring an N-dimensional data object or getting a subtle point across. That said, there is a time and a place for traditional media.

What kinds of IA problems are difficult to solve?
Same as everywhere else: mereology and naming things.
What software do you use and need?
I mostly write my own. There are staples though, like Gephi and GraphViz, and of course Emacs. However, most of the work I do is on paper.
Are there evolving standards for IA?
I kind of hope not, at least as far as a set of prescriptive standards is concerned. However, more awareness on the part of society at large that structuring and arranging information explicitly to abridge effort and facilitate understanding can be somebody's job, I believe will lead to more explicit demand for information architecture.
How do I become an information architect?
Convince somebody to pay you to do information architecture.
What is the Information Architecture Institute and what role do you serve as a board member?
The IA Institute is an organization devoted to the advancement of the practice of information architecture—the theory, tools and techniques. My position has so far centred around the information infrastructure of the organization—a large part, but not exclusively technical. I'm currently in the process of gathering all of the organization's disparate information resources together and making them amenable to improvement by the loosely-knit global group of volunteers that compose the IAI member base.
What would you tell someone who thought of choosing this career field?
Like just about every other creative and/or problem-solving endeavour: you get better results if your eyes are attached to your brain.
What is your educational background? School, Degree/Major? Minor? Concentration?
None. I learned what I needed to learn when I needed to learn it, and continue to. Again, information architecture doesn't have a lot of content peculiar to it. The theory lies in the intersection of so many disciplines that the word interdisiciplinary seems hopelessly inadequate. In practice, it is extremely difficult to avoid becoming something of a domain expert as a byproduct of doing the job.
Do writing skills play a major role in this career field?
Leave aside the fact that writing accounts for a sizable chunk of what information architecture is. Clear writing reflects clear thinking, which is really what people are paying you for.
Are there any resources I should use to gain more information about this career field?
The IA Institute has a mentoring program wherein seasoned professionals volunteer to coach protégés and answer their career questions.