Sarah Perez writes about Dirty Likes:

Steve Cheney, GroupMe’s Head of Biz Dev, explained this problem in more detail in a thoughtful, if pessimistic, post: “Graph Search’s Dirty Promise and the Con of the Facebook ‘Like’.” It’s well worth reading in its entirety. In it, Cheney says:

The truth however is that the link between query intent and your social interactions for interests and places is much weaker than FB wants you to believe.

In computer architecture they call an out of date piece of data “dirty”. Accessing dirty data is bad, wasting time and causing more harm than good. And in this context, much of the structured data that makes up Graph Search is just that: totally irrelevant and dirty.

It turns out as much as half of the links between objects and interests contained in FB are dirty—i.e. there is no true affinity between the like and the object or it’s stale. Never mind does the data not really represent user intent… but the user did not even ‘like’ what she was liking.

He goes on to explain that the problem was created by the way the Facebook “like” system worked. The company told brands that users would see their posts in their news feeds if the users liked the brand’s page on Facebook. So the brands paid big money in terms of advertising dollars to acquire fans. “Across the board big advertisers were told to spend 50% of their ad buy solely on fan acquisition,” Cheney writes. He calls it a “dirty little secret in ad agency land.”

This is why, today, Facebook users can’t just request a coupon, get a free sample, enter a contest, hear about a limited-time sale, etc. via a brand’s page – they are forced to like the page first. This then establishes a connection between the brand and the user. And now Facebook is mining that connection to build its own search engine. Google has PageRank. Facebook has “like” data, check-ins, posts, comments and photos. Here are some of the queries you can perform with Facebook Graph Search, to get an idea of how it will work.

Still seems like Facebook has an uphill battle in trying to separate signal from noise.

Other signals include what I've shared, where I've checked in, and where I've been tagged.

It does seem like Facebook is never going to give up on the Beacon vision.

You have to like a Facebook brand page in order to post a complaint on it. 

That's... Annoying.

You also have to like posts that are sad or angry if you nonetheless want to show support.