Google has rolled out several changes to its search results page - some more impressive than others (maybe I'm just getting jaded). Among the notable improvements:
Larger snippet if you use >3 search terms. In the past, the search results would include a short "snippet" of text, usually no more than 2 or 3 lines, showing your search terms. However, when your query has more than 3 words, a 2-line snippet likely won't even contain all your search terms. So now, if your query is longer than that, the snippets are sometimes 4 lines long. I wish it were more consistent, but at least it's an improvement.
Initial stab at semantic search. To grossly oversimplify (my specialization), semantic search looks for occurrences not only of the words you provide but also words that are similar in meaning. In the past, Google has addressed this with a simple list of synonyms for common words. Put a ~ before a common noun, and Google will search for similar words. If you search for ~moon, you'll retrieve pages that mention the words lunar, Apollo (referencing the Apollo lunar space program), and rising. Nice theory but not so good in practice.
Google has gotten more ambitious, and now attempts a limited version of on-the-fly analysis of search results to suss out words that have similar meanings. The results are still a bit squirrely, but I love the fact that they're working on this. While Google doesn't automatically include results for other search terms, it does suggest alternate concepts at the bottom of the search page, and they're not bad. For a search on quantum physics, for example, the suggested terms included quantum theory and equations, as well as time travel, law of attraction, and what the bleep. A search for Barack Obama gave me suggestions such as Hillary Clinton, John Edwards, and phrases such as barack obama muslim, barack obama middle name, and barack obama smoking.
Obviously, one of the biggest challenges with semantic searching is the computing power needed to data-mine the search results and calculate related terms, on the fly, in a matter of milliseconds.
Search refinement tools. A hiding-in-plain-sight feature was introduced recently -- the "search tools" pull-down option. 
When Google is able to identify related concepts through its
rudimentary semantic search, the search results page will include a
pull-down link that easily enables you to filter your results in
several different directions.
Most of the limit features are what you'd find from an advanced search, but I like having them all there in front of me. And a few of the features were initially rolled out in Google Labs -- the display of images from each search result, for example.
Three items near the bottom of the Search Tools list are the most interesting. Click the "More Text" link and you get..... you guessed it, more text in each snippet. You can switch the search results page display from the standard format to a timeline (also initially introduced in Google Labs).
And see that link labeled "Wonder wheel"? Click there and all the similar phrases, gleaned from Google's semantic search, are displayed in, well, kind of a wheel. In essence, it lets you explore the "trail" of related terms. While this is nothing new to anyone who uses a more visual, clustering search engine, but it's nice to see Google getting on the bandwagon.
So, for example, with my quantum physics search, I clicked the Wonder wheel, and here's what I got:
When I clicked the link at the bottom for "quantum theory", a new Wonderwheel is displayed with the terms related to quantum theory. Click on any of the links in this wheel, and you'll see related terms for that word, and so on.
