On stalker skills scale, I think I'm about a four, maybe a five if I use Google instead of Duckduckgo. And I don't use Facebook anymore so if I wanted to stalk someone, I would be kinda shut out. But if you're a stalker and you're on Facebook, I reckon today Facebook's new social search engine would benefit you greatly.
So far, I have only heard how people and see what you're doing made all the more easier but nothing about not having what you posted kept from any search results.
And Mark Z claimed that ads displayed will not be influenced by the search. I don't buy that. Maybe he's telling the truth about this today but if investor pressure keeps up, FB will eventually turn on that switch and, believe me, there is such a switch.
What's interesting in today's press event is that someone asked FB about working with Google since Microsoft's Bing is involved. FB nicely threw it back and said that it was willing to work with Google so long as they honor privacy of Facebook users.
Nice parry. Still, I trust FB even less than ever.
What's interesting is that from a mobile perspective, I see this benefit users greatly if they're willing to be part of Facebook's sphere of influence. I see apps such as Apple's Siri being asked "what is that Indonesian restaurant that Bob visited last month in Washington?" and the result would come up. Of course, Google can implement something similar with Google Now too.
All in all, I don't see this as a game changer.