Google Semantic Search

Looks like Google has introduced something called semantic search....

(Not my actual key phrase.... Actual phrase has been modified for illustration purposes...)

You know how if you type in a query into Google, Google will highlight your search terms in bold in the search results?

Well, I discovered yesterday that if I do a Google search on the key phrase "how to kill spiders", I see on page 1 of the search results, that 6 out of the 10 results have the words that comprise the phrase "how to get rid of spiders" highlighted in bold, in the title and / or in the text. This also applies to at least one of the Adwords ads above / below the results.

What does this mean for SEO? Is this a good thing or a bad thing?

Could this be a good thing, in that Google wasn't able to find enough relevant results that were optimized for my intended search term, and therefore resorted to the semantic results? Can this be interpreted as a signal that my original key phrase is wide open for pursuing? (Otherwise, why aren't all 10 results with my actual key phrase on page 1?) Is this a sign that this presents an opportunity to rank?

Could this also mean that I should also strive to rank for that semantic phrase?

OR, could this be a BAD thing, in that Google is going to start ranking sites based on semantic relevance and not just based on the actual key phrase?

I don't know whether this semantic search was implemented before or after the recent Penguin update. I only just noticed it when I was checking on one of my websites after it had dropped 20+ places in the search results for the key phrase "how to kill spiders" I was trying to rank for.

Any thoughts?