Maybe Facebook might end up being the Xerox PARC of our modern times.
I'm not trying to discredit what Facebook is doing, or the people there, but it'll take time to build up to that level of talent. Having a few remarkable individuals is a great start. Having an entire department filled with them is going to be hard work.
Bell Labs made significant contributions to Physics (solid-state and optics), Chemistry, Electronics, Computer Science (operating systems, graphics, speech recognition, networking), Materials Science, Communications (here they pretty much invented an entire field of study) and the design of so many everyday things (they had an entire team that focused on just the design of your telephone wire) that is would be impossible to imagine what the world would be like if they didn't exist.
If Google didn't exist, search would still have been solved, maybe a decade or so later. If Claude Shannon didn't work at Bell Labs when he did, it could well be the case that we wouldn't have come up with such an elegant theory of Information even today, and therefore the world would look nothing as it does.
Facebook has been around very little time by those standards, and Google only slightly longer.
Time will tell if Facebook, Google and Microsoft can live up to their contemporaries.