Since the MySpace container does not yet support User Data or Activities, what you want to do will probably have to be managed by an external application server. I've been struggling for days to get some sort of persistent storage going with the MySpace implementation of OpenSocial only to find out that they don't support half of OpenSocial yet. That doesn't mean it can't be done, it just means you have to move persistent storage off of OpenSocial and access it via a call to makeRequest - similar to the RSS feed example someone posted above (except RSS is passive and you can't communicate changes to it, which is what would be required for a blogging application). You can make a call to a php, asp.net, perl, xml, you name it, application to provide the data. You would also have to provide an interface for updating of data and wrap that all up into some security token, probably the myspace friend id and auth token (to prevent hacking and unauthorized access of data).
So, your architecture will look something like this:
Your Band Gadget <==> MySpace API Servers <==> Your Application on another server
Hope that helps with your design. Drop me an email if you want to discuss anything more in depth.