Most sites are easy to relate to popular or important link rich ideas if you are creative. For example, to some people this site relates (or at points in time related) to web browsers, open source software, religion, politics, science, education, human rights, free speech, marketing, market manipulation, entrepreneurship, blogging, search, and many other link rich topics.

Part of why I stray off topic is because I think everything is related. But it also doesn't help that I entered the market so late, and SEO is generally hated when compared with the general linkability and passion with which people talk about innovating search technologies. What can you do to make your site relate to something people care a lot about or are irrationally / emotionally drawn toward? Do you care about the environment? Are you religious? Are you disabled? Are you part of a minority? Do you care about human rights? Do you wish the world was safer? What flaws in Google's business model concern you? How did you overcome your biggest faults and fears? Could you help stop wars?

The things you are not supposed to talk about are the things which link rich people link at. You know your idea has legs when people at different ends of the political spectrum link to your idea and claim it as their own because they identify it as being associated with their ideology.

Typically it helps if most of your content is focused on your core topic, but some of the people who are easiest to talk about are easy to talk about because they can relate their topic to other hot topics. If you are a usability consultant why not talk about blogging and search, for example.

Focus on the reader. Controversy will incite passion. Passion drives links.

You have to balance it though, because packaging matters:

At some level, at a very major level in fact, the way we feel about a transaction is more important than the transaction itself. Some people like a sporting event more if they got the ticket from a scalper, other if they got the ticket for free from their boss. Some people need to feel like they've taken the system (whatever the system is) for everything it's worth. Others need to pay retail (especially on a wedding dress, cemetery plot or flu shot).
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Marketers are working hard to corrupt the way we feel about our friends and the people we respect. I think, in the end, it's not going to work. We're hardwired to respect real authenticity, and at some level, that means trusting the motives of the person we're listening to.