The competitive landscape surrounding Google gets more and more interesting by the day. Now two of its rivals, one of which is being run by someone who probably knows Google’s inner workings more intimately than most of its current employees, are talking about teaming up.

Apple and Yahoo are said to be in talks about possibly integrating Yahoo products more into iOS, the the operating system powering the iPhones, iPods and iPads in millions of hands.

Should Google be worried? What would you like to see out such a partnership? Share your thoughts in the comments.

Any increased integration of Yahoo into iOS would only add on to existing Yahoo Finance and weather data that come on the operating system today.

The Wall Street Journal is reporting that the two companies have been “discussing how more of Yahoo’s services can play a prominent role on Apple’s iPhone and iPad devices,” citing people briefed on the matter. Such possibilities could include, according to the Journal’s sources, “more content from Yahoo News and its other web properties loaded onto Apple devices or available through an expanded Siri partnership.”

A deal is not imminent, the report says.

The Journal isn’t the only publication with sources talking about this. Bloomberg cites “a person familiar with the matter” as saying executives from both companies have “discussed ways to collaborate more closely on mobile software”:

Yahoo Chief Executive Officer (and longtime Googler) Marissa Mayer has met with Eddy Cue, Apple’s senior vice president of Internet services, to explore ways Yahoo can be more deeply integrated into the software that runs on the iPhone and iPad, said the person, who asked not to be identified because the talks are private.

Mayer has been very clear about how important mobile is to the company’s strategy going forward since she took over as CEO last year. This would obviously be a huge step in making sure smartphone users are accessing Yahoo content on a regular basis. Depending on what kinds of integrations we see, it could turn out to be a pretty big deal for Yahoo’s piece of the search market as well, and would give Yahoo an interesting partner should the Microsoft alliance fall apart.

The part about Siri is particularly interesting, and that could mean any number of things. One thing it can at least enable us to imagine is a search-related partnership. Yahoo, of course, outsources its search to Bing on the back-end, but Yahoo’s relationship with Microsoft seems to be souring. Apple’s with Google, meanwhile, is too.

Yahoo has expressed how important search still is to it as a company in recent months, and now they have one of the biggest names in the search industry running the show. It was a different story when Yahoo went the Bing route.

The Motley Fool even makes an interesting case for why Apple should (but probably won’t) just buy Yahoo. “Yahoo! already provides some of the default iOS apps for stock quotes and weather. Perhaps more importantly, Yahoo! isn’t Microsoft or Google,” writes Rick Munarriz. “Mr. Softy and Big G are Apple’s two biggest rivals, though these days Google has become the bigger enemy as Android conquers the smartphone and now tablet markets. Apple tried to distance itself from Google last year, going with a homegrown default solution to Apple Maps.”

“Right,” he continues. “We know how badly that played out for Apple. Any bone that Apple could throw Yahoo! is one less bone that it would either throw out to Google or possibly mess up on its own.”

I don’t expect any acquisition announcements to be made anytime soon, but it’s interesting to consider.

Even with the right partnership between Apple and Yahoo, Google could suffer significantly in terms of search market share. Let’s not forget that Yahoo used to rule the search space, and now it has a seasoned veteran from the current king of search running the show. What if iOS made its way to using Yahoo as the default search? How many would bother to change it to Google?

Google and Apple have had a search deal in place for about a decade. Few details are known about this deal. Greg Sterling at Search Engine Land recently shared a couple of analysts’ theories:

An analyst at Macquarie Capital estimated that Google was making $1.3 billion annually in paid search revenue from iOS devices. Macquarie speculated that Google returned about $1 billion of that to Apple as part of the agreement that made Google the default search engine on the Safari browser….Another financial analyst has come up with a similar annual estimate of the value of Google’s default iOS search deal with Apple: $1 billion. Morgan Stanley’s Scott Devitt is responsible for the new estimate…Devitt disagreed with Macquarie, arguing that the structure of the relationship is probably not a “revenue sharing” deal but instead a straight fee-per-device payment from Google to Apple. Devitt believes that Google pays Apple roughly $3.20 per iOS device, which would avoid the accounting issues arising from a revenue sharing agreement.

Sterling himself wrote, “While it’s extremely unlikely that Apple would try and make Siri into a full-fledged search engine, it could significantly beef up Siri’s content search and discovery capabilities. In that capacity, Apple might be able to siphon off selected commercial queries in key categories such as local, travel and entertainment.”

As we have discussed repeatedly, including in this recent article, the biggest threat to Google’s search market share is the gradual chipping away at it by various vertical services. Even if Yahoo only supplied some of the content on Siri (regardless of whether it became the actual default search on iOS), Siri could continue to improve with increased integration across other services, and rendering Google less of a need for users, little by little.

Obviously, how this really plays out is anybody’s guess. Apple and Yahoo may not even expand their partnership at all, when it’s all said and done. Still, if I were Google, I might be a little nervous about what these companies are discussing.

Should Google be worried? Let us know what you think.