The social-graph is a reduced set of the internet. It is probably easier to search, but how will the results be better than Google?
With Google's velocity, I think they're probably going to get to "social search" first (good luck to Blekko, but reliance on FB is not going to scale - especially when FB looks to monetize - social search is their meal ticket).
You have control of your own social graph, you don't have control over who puts a page up for Google to crawl. You're using the authority someone has as part of your network to filter what comes in to the network - search only on sites that friends-of-friends have recommended and you're unlikely to get spam or sites that are hard to navigate or that won't provide a good service. If I'm looking for new outdoor equipment I could look at the online stores that fellow scouts have used and recommended and so save time weeding out the better stores.
Just my immediate reaction to your question. There are clearly benefits in both types of search. Also this presupposes that FB aren't trying to inject advertised offerings in to your social-graph based search; probably a bad assumption as that there looks like gold to me.