I have early access to the preview but there is literrally hundreds of write ups on how it works and why it works as it does.
In summary, watch this video:
Should SEOs take notice? Of course they should. But we are only at the early stages of what Facebook Graph Search can search. Right now it is limited to people, photos, places and interests. It does not have events or posts enabled in search or many of the other gated Facebook content.
So the most important aspect for SEOs to take notice on is the places. Making sure local businesses come up. How? Clearly location and likes are important.
I should note, Bing also gets a play here when it falls outside of people, photos, places or interests, Bing is the search engine. More at the Bing blog.
To try Facebook Graph Search yourself, sign up for the beta over here. It may takes days, weeks or months to be approved.
Forum discussion at WebmasterWorld.