One thing is for sure though. Google has been introducing a lot of additional features to its search engines to introduce personalization into their search results. Google Starred Results will definitely bring the level of personalization in search to another level.
It just means you bookmarked it while logged in as a Google user, or you hit the Up arrow on it , I don't know which but it has to do with your personalized results when logged in.
star rating is to improve personalised searches. When a user clicks on the star google will know that particular likes the result and will rank it higher for that particular user.
Whenever I am signed in with my google or blogger account, I come across such stars. Also if you or anyone around you with the same ip address has hit the up arrow, it will show up in the results. I doubt it might show up in any other location.
Actually I just found the answer while I was reading Matt Cutts' Blog: http://googleblog.blogspot.com/2010/03/stars-make-search-more-personal.html
I think the bigger question is whether or not the number of times a website gets starred will help it to rank better overall. Afterall, it's another measure of a site's popularity and a measure of how well it fits the search term. But, we'll never know because if G told us that it helped, a whole new industry would arise, "pay-per-star".
I don't think Google would ever make that manipulate the serps. but..just in case, maybe someone should buy starfarm.com.