It has been an interesting few days watching Silicon Valley’s most powerful company, Google, fend off technology’s latest adolescent darling, Facebook. That of course, is what Google’s (GOOG) OpenSocial initiative is all about, pitting its new-born social networking platform against Facebook’s six-month-old social networking platform. And while these two companies battle it out for the opportunity to capture our time with the useful as well as the utterly inane, the people caught in the crossfire are guys like Ali Partovi.

Partovi is the CEO of iLike, an online music discovery site that happens to be among the most popular Facebook applications. Like many of the apps on Facebook, the one-year-old iLike began life as a web site, trying to attract an audience and build its own social network around the subject of music – what are you listening to? check this out, are you going to this show? You get it.

iLike struggled to find that audience until it put up a widget on Facebook. By tapping into Facebook’s massive built-in membership (now approaching 50 million), the music application was quickly downloaded by a few million people. Today, it is the sixth most actively used widget on Facebook with 611,599 people swapping music tidbits daily. That makes iLike the No. 1 Facebook music application.

You would think Partovi might stick by his Facebook pals, but he’s happy to take his set of music toys and also play with Google. The search giant’s OpenSocial initiative is creating standards to allow widget makers like Partovi to tap into all social networks that are part of the Google alliance. Rather than crafting a different application to meet different standards at each social network, he just does it once. “OpenSocial is the best thing that possibly could have happened to us,” Partovi says. “There’s no incremental cost to developing for all these different networks, but there is the incremental benefit of being everywhere.”

Developers like Partovi are the first to tell you that they are all about creating new widgets for the platform that has the most people, makes it easiest for them, and pays them the most. Very few third-party applications on Facebook are making any real money, and it remains to be seen if there is much of a business there for anyone but Facebook and a handful of top independent developers like iLike. But even iLike, RockYou and Slide understand that Facebook by itself isn’t enough, so they’re all going to OpenSocial.

Their move to different networks may help answer the question, who owns the user? Is it the social network or the widget makers? Slide founder Max Levchin is building his business around the idea that he owns the user. So is Partovi. But so is Facebook founder Mark Zuckerberg. It will be interesting to see if Facebook members follow Partovi to LinkedIn, MySpace (NWS), Bebo, Hi5 and the other social networks that are going Google. It may well be that there are enough social network addicts around the world to go around, but it seems more likely that one network wins at the expense of the others. Just ask MySpace.

For now, guys like Partovi are sitting pretty as platforms compete for his attention. But there are signs that the things could get ugly fast. There are persistent rumors that Facebook is about to launch its own music application that would compete with iLike (now there’s a play from the Microsoft (MSFT) platform book). That is the danger of building a business on top of someone else’s platform. It’s theirs, and they will do with it what they want.