One, I had never heard of Ostrom before and her inclusion (she is a political scientist) is further evidence of the economics prize slowly morphing into more of a social science prize. Many have figured it would undergo such a transformation given that it has caught up pretty well with all of the old stuff and either has to become very contemporary or more broad.
Two, any modern economist is very familiar with Williamson's work as it is fully entrenched part of the canonical PhD curriculum - especially if you study industrial organization as I did. His work explored the black box of 'the firm' which prior to his work was simple an entity that too inputs and transformed them into outputs. But what are the internal incentives of the firm? What are the principal-agent problems of firms? Where do firms stop and why? (Or to put this last one in clearer terms - why do firms exist at all, why don't they just contract with private individuals?)
Perhaps the heart of the work is in institutional decision making in the absence of markets (or in the presence of institutionally created markets). This is very timely, as the internal incentives of Wall Street firms were seriously skewed and are largely responsible for the collapse of worldwide credit markets that set of the current crisis. These incentive problems need to be addressed institutionally through a renewed set of modern regulations and the place to start thinking about these issues economically and politically is with Ostrom's and Williamson's work.