Twitter announced some new improvements to its Discover tab today. It’s getting more personalized, and will begin surfacing content based on tweets that are popular among people you follow and who they follow.

“The Discover tab’s new design shows who tweeted about particular stories,” explains Twitter VP of Product, Satya Patel. “You can click ‘View Tweets’ on any story to see popular Tweets from your network or recent, relevant Tweets directly below the story summary. This social context helps you understand why each story matters to you and makes it easier to join the conversation. You can reply, retweet or favorite these Tweets, or you can ‘Tweet this story’ to share your own perspective.”

There’s an interesting post on Twitter’s engineering blog talking about the back-end of how the features work. “Behind the scenes, the new Discover tab is powered by Earlybird, Twitter’s real-time search technology,” explains Twitter Director of Engineering, Ori Allon. “When a user tweets, that Tweet is indexed and becomes searchable in seconds. Every Tweet with a link also goes through some additional processing: we extract and expand any URLs available in Tweets, and then fetch the contents of those URLs via SpiderDuck, our real-time URL fetcher.”

“To generate the stories that are based on your social graph and that we believe are most interesting to you, we first use Cassovary, our graph processing library, to identify your connections and rank them according to how strong and important those connections are to you,” Allon adds. “Once we have that network, we use Twitter’s flexible search engine to find URLs that have been shared by that circle of people. Those links are converted into stories that we’ll display, alongside other stories, in the Discover tab. Before displaying them, a final ranking pass re-ranks stories according to how many people have tweeted about them and how important those people are in relation to you.”

This might be useful information to know if you’re thinking about engaging in any realtime SEO strategies. Twitter is probably the go to place for a lot of people looking for realtime info and commentary these days, especially now that Google no longer has realtime search (thanks to the expiration of a deal with Twitter last year).

Twitter’s efforts in this area represent a real point of competition for Google. Not that Twitter and Google are competing on search in general, but Google’s greatest threat is users’ decreased reliance on it for various search tasks. Google’s lack of realtime search has to be driving some amount of searches to Twitter. I know it’s driving plenty of mine there. If I need to find up-to-the-second info or commentary on a subject, I can’t rely on Google for that without realtime search.

See: Gaddafi Shows Why Google is Failing Its Mission in Search

Google has put a great deal of emphasis on freshness of search results with various algorithm changes over the last six months or so. That combined with Search Plus Your World (the personalization element, which draws significantly from Google’s own social network), I believe is Google’s attempt to compensate for the lack of realtime search, at least in the short term. Comments made by the company in the past indicate they’re hoping Google+ can eventually provide the same kind of realtime power that Twitter can’t, but the user numbers just aren’t there. Not for the “social destination” part of Google+ (as opposed to the “social spine” part).

So, Google is jamming “fresh” content into organic search, sometimes at the cost of relevancy. It’s not working as a substitute for realtime search. For one, when Google did have realtime search, it was its own section in the search results, not unlike Google News results (or other types of Universal Search results) are today.

“All of this happens in near-real time, which means breaking and relevant stories appear in the new Discover tab almost as soon as people start talking about them,” says Allon of Twitter’s offering.

That’s important, especially for journalists. And it’s something Google can’t provide in search results without the realtime search element – without Twitter. Until people start using Google+ like they use Twitter, it’s just not going to happen, or unless Google can get back that Twitter firehose.

Twitter says the Discover tab update is only part of the company’s ongoing development of the feature. In other words, Twitter is working on getting even better at finding ways to get relevant, realtime info to users.

The Discovery tab updates will be rolling out over the coming weeks on Twitter.com and the Twitter iPhone and Android apps.