Not quite like reddit and digg. You can bot farm those because the lists are common to all.
In this search engine, let's say there's you, me, person three, and spammer. You you are following me, and I'm following person three. Spammer isn't in any of our networks.
When you use the search engine, you only see results that you, me, or person three manually tagged as worthwhile. Any pages or content that Spammer tagged as worthwhile aren't part of your results, because they aren't in your network. So they can try to game the system all they want, but it won't affect you.
If person three starts following Spammer, I can unfollow them and then Spammer's results will no longer be included in your search results (or you can unfollow me and avoid those results).
I imagine rankings would also be affected by degrees of separation, so even if you followed me, I followed person three, and person three followed spammer, results tagged by me and you would take much higher precedence than results tagged by Spammer.
This also allows you to make custom searches by choosing which people you follow to include. Suppose you want to search for good headphones, so you make a search, but only include people in your network that you know are music and audio savvy, so that the results reflect the pages tagged by those people.