Earlier quoted context omitted.
If we compare whether Facebook or Google can be more easily replaced I could argue that Google has a higher chance of being replaced because some startup can come along and build a better search engine for less than 1% of what it cost Google. Whereas I don't see Diaspora really being much different than a Jabber protocol with social networking features. Jabber didn't kill any instant messager protocol, it just furthe…
Google will be replaced but not by search engine like better Google . There will something completely new, like visible now in mass personal computing shift from desktop (Windows) to mobile (it looks like the Android is next main OS). The great question is what will push Google into oblivion.
More and more internet activity is taking place in 'closed-wall' communities like apps and Facebook that Google Search can't touch (and, hence, can't monetize) for the most part. This trend is gaining real traction as it seems well equipped to satisfy folks' demand for better, more relevant filters. The power of social networking to help build and refine such filters is pretty telling... just think about how much of your 'news' you get off your Twitter or Facebook feed.
Unless Google figures out a way to penetrate closed-wall communities (via strategic partnerships, licensing of some sort or whatever) or innovate some super useful product that brings in revenue on the scale of AdWords (GoogleMe?), we'll probably see a piecemeal dethroning happen.
This is probably one of several reasons why smart people are migrating from Google to Facebook.