There's still no indication of what the app will be, but Joe seems to be a bit upset that he broke Microsoft's new rules to "just shut-up 'til ship" (sic). He went on to tease more interesting things in the pipeline, saying that this week "could be a pretty good app week here", but that it's "hard to know which publishers will hit which dates".
And, in case all you non-US users haven't been too excited with the release of US-only Pandora, Joe wants you to know that "this week is NOT a US-only kinda week. :)"
We'll let you know when we find out what apps are coming.