Microsoft (NASDAQ:MSFT) had better keep a close eye on its new search partner. Yahoo! (NASDAQ:YHOO) doesn't seem completely committed to this relationship.

This week, Yahoo! announced a slew of improvements to its market-leading Web-based mail service, its instant messenger, and -- tellingly -- the Yahoo! Search experience.

Everything is becoming more social. The company is adding photo-sharing features to Mail and Messenger, helping you follow your friends' Twitter updates while reading your mail, and filtering emails from your friends to the top of your inbox. High-definition video conferencing sounds like a low-budget take on Cisco Systems' (NASDAQ:CSCO) TelePresence product, and there's integrated support for sending cash through eBay's (NASDAQ:EBAY) PayPal payment system to your mail contacts.

But like I said, perhaps the biggest update is happening in the search space. The new Yahoo! Search interface, which will roll out to users everywhere over the next few months, helps you reorganize search results in a variety of new ways. In a single click, you can restrict results to ostensibly trusted sources like Wikipedia, self-help site eHow, (NASDAQ:AMZN), or Google's (NASDAQ:GOOG) video destination YouTube. There are also improvements to the search engine under the hood: Yahoo! tries to figure out what you're looking for based on your recent search history.

All of this is presented in a redesigned interface that reminds me of Bing more than anything. (Hey, that rhymes!) And Yahoo! is doing it "to prove just how committed we are to continued innovation in your search experience." I believe that’s a thinly veiled slap in Microsoft's face. Yahoo! may be entering this relationship, but it won't bend over backwards for its new partner. It's also a bit of an homage to the coming partnership, so Microsoft isn't likely to complain in public.

But I'd love to be a fly on the wall in Redmond at Microsoft's next board meeting. Are we gonna be left at the altar? Is Yahoo! going it alone after all? And those fears won't subside until the final nuptials have been signed. Cheeky move, Yahoo!. There's life in you yet.

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Fool contributor Anders Bylund owns shares in Google, but he holds no other position in any of the companies discussed here. You can check out Anders' holdings or a concise bio if you like. The Motley Fool is investors writing for investors.