Facebook VP of Technical Operations, Jonathan Heiliger, talk in this video about balancing innovation and building a stable infrastructure for rapidly growing userbase. 

...sometimes we air to aggressively on the side of innovation and iteration and put things out on the site in perhaps a small quantity that may break the site or cause the site to slow temporarily and other times we air on the side conservatism, of not releasing new functionality or new feature, and that then delays the sort of user gratification of having that feature or fixing that bug.

It's part of CNET's excellent CIO Sessions, check out all the videos here.  They don't go too dive too far down the IT stack, however they do a great job of framing many of the issues that CIOs are struggling with.