I didn't pay much attention to this facebook graph search, and frankly it doesn't seem like it's all that useful in its current stage. I just realised, though, how much of a threat it poses to google and all other general search engines.
Google is amazing in its sheer breadth and size. It mines data from billions upon billions of sources. And yet, to what extent do people really use the power of google? I'd bet that a large portion of google searches are just simple practical every-day life related searches, like looking up restaurants/stores in a certain area, finding doctors, researching information for travel plans. Probably another big portion is to look up answer for common questions like household problems, health issues, etc. Of these two areas, I predict that facebook will completely take over the first one. Google has an immense breadth of sources, but facebook has what really matters: social information about you, and the ability to provide you with search results by using your and your friends' social information. Reliability by using the people you know and trust.
Right now, for example, I am making plans for a holiday in the philippines. As an avid user of google, I am very happy to go look through 20 links, and read up on reviews and articles pertaining to the security ratings and general ratings of every filippino airline. It's not too time consuming for me, but it may be for people who are not as agile with the internet. Now think about facebook graph and what you'll be able to do with it as they keep developing. I am concerned with the security of philippine based airlines. One way is, as I mentioned, to do an exhaustive internet search and read writings of people I don't know (but can trust to varying degrees based on their writing, and on the website in question). Another option is to do a facebook graph search for friends who have flown in the philippines. Which airlines did they choose? Maybe I want to narrow down the search a little bit. Look up only friends whose judgement I trust. Maybe I can, as part of the search options, limit my search to people from a certain group in my university, to a branch at my workplace, to my family, etc.
I think that as the facebook-using world keeps going, facebook is going to own more and more information of better and better quality. In my fantasies, this will fuse with nano computers and a proof that P=NP, to create a climax of the age of information. A race of virtually-omniscient men. (virtually, here, works in both senses of the word ;)). Although -- at that point, the information technology wouldn't really have anything to do with facebook graph search anymore, lol.