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My wife, two kids and I each have our own MobileMe email addresses and our own iOS devices. We independently sync our own email and calendars. Currently, we can each purchase games and share them by downloading them for free on each device. You simply take your iphone and switch to the other family members iTunes account before you try to download the game and it lets you re download it for free. Then, once the game is on your iOS device, you can download the updates when they become available by entering in the original purchasers username and password. I can't imagine that it will be any different. However, this currently doesn't work with music but it appears that this is about to change when the new cloud service is released.
 
My wife, two kids and I each have our own MobileMe email addresses and our own iOS devices. We independently sync our own email and calendars. Currently, we can each purchase games and share them by downloading them for free on each device. You simply take your iphone and switch to the other family members iTunes account before you try to download the game and it lets you re download it for free. Then, once the game is on your iOS device, you can download the updates when they become available by entering in the original purchasers username and password. I can't imagine that it will be any different. However, this currently doesn't work with music but it appears that this is about to change when the new cloud service is released.

downloads are automatic via cloud then
 
I'm running into the same issue. Wife and kids using the same iTunes account for years for all purchases. Because of the new iCloud and syncing features, I wanted to "wean" my kids off of my account and onto their own or let them use the old account and I create a new one.

As far as music goes, if everything form iTunes is non-DRM (or ripped), then playing the songs and syncing them to any device shouldn't be a problem. The authorizing of the computer is only for DRM'd songs.

The issue with the music is, when I created a new account, all the songs I purchased on the previous account do not show as a previous purchase. But, would they sync anyway with the song matching feature?

With the apps, they seem to be locked to the account that purchased them. This is where I'm leaning to letting my kids use the old account and I use a new account and delete and re-download my apps under the new account. It would cost me a little over $40 for apps that I purchased. At least all my apps would be associated to my new account. I don't want to have to keep changing accounts every time I need to update applications.

I sent an email to Apple about this situation and I'll see what they say.

Without knowing anything else right now, I'm leaning towards the new account for me and repurchasing the apps and hope that the song matching will let me sync all my music to my various devices.
 
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