I've got a reason... I have some apps I want to create that will work across devices, i.e. WP8 and W8 (and technically even Android and iOS). Until we have the WP8 SDK this is only possible with herculean effort, since you can't really use the WP7 SDK on W8, and you can use WinRT anywhere except on W8. Further, the portable library support is also going to be much improved when WP8 SDK is available. So, I'm in a holding pattern until I can get the WP8 SDK.