I was not formally interviewed, as I was referred by a previous employer. The interview was informal but in person, and involved a couple of hours walking around and discussing technical experience and solving particular technical problems.

What language/technology would you use for this, and why?

We have this problem in our current release. How would you research and address this on the job?

One of the harder parts was the process of getting the position. It can take a while for a new position to be approved.

The interview was in the form of a conversation and not particularly formal, so I can't really pinpoint the most difficult question. I believe my experience to be atypical, but in general, be ready to jump on technical problems, ask questions about the team, be familiar with the type of work you want to be hired for, and be ready to discuss any related topics.