Tim Heuer is discussing the issue of hosting Silverlight applications (XAPs) on your site that are from a different domain.
What I mean here is that your site (www.coolwebapp.com) has an <object> tag for Silverlight plugin that has the Source parameter set to apps.anothersite.com/foo.xap. This is essentially the cross-domain hosting situation. What happens in this situation is that the plugin loads but the app does not, presenting in just a big blank space where the app should be.
A recent head-banger sent me a note and I sent him my items to check on how to solve this. I thought I’d share.