Power of a Department Chair? What powers does a Department Chair have in a University setting? For instance, is a Dept. Chair the "boss" of a tenured full professor within the department?
This varies quite a bit between universities and colleges within the US and probably even more when you consider the academic systems in other countries.

In some cases (particularly in smaller departments) the department chairmanship is a rotating assignment and whoever is currently the chair won't be the chair in a few years.  This means that they have to get along with all of the faculty in the department or risk retribution after they step down as chair.  In this system, although the chair is formally the head of the department the chair often has little authority over the budget (the department might not have an independent budget), hiring, and other important decisions.  The chair will typically consult with all of the senior faculty before taking any significant action.  I've served as a department chair in this system and I can assure you that it is totally unlike being a manager in industry.  

At the other extreme, there are places where the department chair is a permanently appointed full time administrator with substantial control over budgets, hiring, and all important decisions.  These chairs have a lot more power, but even then senior faculty members may be largely independent of the chair's authority by virtue of their fame, grants, etc.