A few key points of differentiation between MySpace, other OpenSocial "containers" and Facebook are as follows:

• Apps on the Home page.
I believe that one of the biggest reasons Facebook apps have such low user engagement numbers is because they can't enter the key space of the user admin page. That's where users live, not on their own public facing profile pages. MySpace is hoping to go so far as to create an "everyperson's Netvibes/PageFlakes/MyYahoo" experience.
• Custom namespaces
MySpace has a long list of custom namespaces that aren't available in OpenSocial's most basic structure. That's the case with almost all OpenSocial implementations, we hear, and it will be interesting to see how real the promise of interoperability is.
• Synchronous communication
It may not be XMPP but the MySpace app namespace ONLINE_FRIENDS appears to let app developers access the sub-list of a user's friends who are actively online. Many social activities are best done in real time (like asking for money via Lending Club? maybe not) and we'll be interested to see what apps make use of this option.
• OAuth support
MySpace users are going to be happy to share their contacts and info from other applications off-site with apps on the MySpace platform because they'll be able to do so securely. MySpace is about to become the biggest use-case of the oAuth authentication protocol, something many sites are scrambling to implement. Will app developers put this to use? We'll see.

The Other Side of the Story

MySpace user numbers dwarf Facebook's, but developers may have dampened enthusiasm for this platform. MySpace users don't have the yuppie gleam that Facebook or LinkedIn users do, and after a few months the Facebook platform has been a let down for many people who were beside themselves with enthusiasm over it at launch.

Will app spam become an issue at MySpace the way it has at Facebook? Facebook has lost a lot of user good-will over app spam, something they are focused heavily on changing. MySpace has largely killed the messaging spam that plagued its user experience for so long, I don't imagine users will be happy to see something like it back again.

Facebook has already moved beyond where it was a month ago, when the MySpace developer community launched. Facebook apps will soon live off-site, all over the web, for example.

Today's beta launch is definitely worth a look. Will it be as mutually beneficial for other sites as the YouTube platform is likely to be? That's doubtful.

None the less, today marks a big turning point in the history of the dominant social networking site and a company that once told outsiders the following:

“If you look at virtually any Web 2.0 application, whether its YouTube, whether it’s Flickr, whether it’s Photobucket or any of the next-generation Web applications, almost all of them are really driven off the back of MySpace.” MultiChannel News is reporting that Peter Chernin said there is no reason why News Corp. couldn’t build parallel businesses, targeting YouTube in particular. “Given that most of their traffic comes from us,” he said, “if we build adequate if not superior competitors, I think we ought to be able to match them if not exceed them.”

So much for that strategy!