Did you see this link just posted today?
http://windowsteamblog.com/windows_phone/b/wpdev/archive/2012/09/12/windows-phone-8-sdk-preview-program-is-now-open.aspx

>So, I'm downloading the Windows Phone SDK 7. Don't ask why.
>
>I don't know.
>
>How different is developing for 7 and 8?
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>Is there any way to know until it's released?
>
>I don't really want to learn something that's only going to be relevant for another two minutes.
>
>Which is why I should probably continue ignoring Microsoft.
>
>But if anyone can sort of explain how the the process of developing a Windows Phone 8 app changes from the process of developing a Windows Phone 7 app that'd be worth a start.