I attended Tech Days in Ottawa, Pandora + multitasking was raised. MS is listening. Apparently Pandora will be one of the first 3rd party apps to be allowed to run in the background (that is native to the zune software). So if your app is as popular as Pandora, they may make an exception for it too: good luck!

I was told at Tech Days that once you insert SD card, the OS consumes the memory, and won't give it back. If you remove the card it will brick the device, you need to have the OS re-imaged, loosing your data.