good luck trying to play project gotham with an ipod
MS have clearly stated that all controllers for the 360 must have the correct unlock code on them which must be licensed. This will more than likely also include any periferal MS want's to manopolise on, such as the usb WIFI dongle, memory cards and any up and comming mouse/keyboard/webcam any devices that MS can not or are not going to sell specifically for the xbox, such as an ipod, digital camera etc have had drivers coded into the correct application such as the media player.
Remember USB doesn't mean it doesn't need drivers.
As far as getting old joypads working on the new xbox, you can bet that soon after launch some company in taiwan will release an unlicensed adapter for all manner of controllers, PS2, xbox etc.
And one thing to consider with saves is that a lot of xbox games now lock the saves to that xbox so you can't even migrate to another xbox let alone a 360.
I was wondering about the new live system logging your progress and such, so it almost seems like part of your game save is being recorded by live.