Its an interesting comparison, but I think at least part of the difference lies in the fact many of google's main services -- search, maps, shopping, news -- ar

Its an interesting comparison, but I think at least part of the difference lies in the fact many of google's main services -- search, maps, shopping, news -- are about getting you what you want and away from google. The faster you're done using google, the less time you spend there, the better they're doing. Gmail and apps are more time consuming but I think a certain level of "well, I have no choice to do the this work or not, I might as well have a nice interface" comes into play when using those. Google's tools seem more about facilitating accomplishing something else as fast as possible, while facebook is the ends in and of itself. How long you spend on facebook is the metric of how well facebook is doing. At least thats my take on it.