Fog Creek is a take no prisoners kind of firm with questions that will draw primarily from the data structures and algorithms. Be familiar with C as well as with a mainstream OOP language such as Java/C++. Other than that, the interview questions are fairly standard and of the same variety you can expect from Google or Amazon. Be prepared! My mistake was not reviewing enough of the relevant material. Seems like a great company to work for though with a solid grasp on the concept of best practices (thanks, I'm sure, in large part to the prominence of Joel Spolsky).

Fog Creek is has the most organized of screening process I could imagine. Really shows that their core competency is project management software. The interview process was described as five 1-on-1 technical interviews. The interviews are strictly technical, and result in a hire/no-hire vote within hours. As long as I make it through the 5 without getting two no-hires, then the next step is a job offer. I participated in one technical interview, writing javascript code on a shared whiteboard. I answered all questions and solved the problem to every level of complexity asked. The hour went fast, and at the end I asked if there was any other problems or details he would have asked if we had more time, and he said no, I had answered everything he had. Then I got the goodbye form letter. Apparently that guy's vote counted twice because I was out.