The second is longer snippets for longer queries.
Let's look at the first change first. The yet-to-exist semantic Web is one that is all about relationships: the understanding that everything is connected to everything else, and that these connections provide a meaning that goes beyond the meaning for any one element in a vacuum. My favorite metaphor for the semantic Web is one in which I can Google "Who is Darth Vader's son's sister?" and get, of course, "Princess Leia" as a result.
Google's newest upgrade takes a step towards this, but right now it comes across as more of a Mechanical Turk or Mahalo scenario: your query may or may not be one of the ones that has additional queries associated with it.
On the other hand, Google describes the change on its Official Blog as "a new technology that can better understand associations and concepts related to your search," and the improved associations as "one of its first applications." So it sounds like there is an algorithm component here, which may ultimately lead to that Holy Grail of meaningful interpretation of relationships.
(Incidentally, my Google search this morning for "Who is Darth Vader's son's sister?" was fruitless.)
The longer snippet thing is a response to the lengthening of the average query. Google's snippets show your query in context, with the search terms in bold. That's difficult to do with a two-line snippet when your query is "earth's rotation axis tilt and distance from sun." With a three-line snippet, however, a whole new world opens up.
There is a bigger point to be had here: one relating to habit and mindshare and perceived value. In his coverage of the announcement, Motley Fool's Anders Bylund points out that Google is really only playing catch-up with Yahoo, and that "Yahoo is arguably doing it better." So if semantics matter, how come there hasn't been a mass exodus to Yahoo?
The answer is simple: there are precious few of us outliers who notice incremental changes like these; even fewer would change our search habit as a result. Switch engines for a three-line snippet? Not on your life.
Without a doubt, Google must continue to implement improvements like these; in a vibrant marketplace, the only two choices are growth or death. On the other hand, these incremental changes are the equivalent of treading water in the oligopoly that is the search industry. Their impact on search share will be immaterial.
The war for search will not be won or lost on incremental algorithm changes. A significant difference in the search landscape will only come from a major disruption, one that makes users stop, think, and engage their prefrontal cortexes. Without that, things will pretty much stay as they are.
What kind of differentiation would make you change search engines?