If you are one of those people eager to sign up to iTunes Match, you may run into problems if you share your Mac or PC with another person in your home. We have one Mac and a number of iOS devices, including an Apple TV (gen 2). Unfortunately, you can only use one Apple ID on a device every 90 days with iTunes in the Cloud. So, if my wife downloads a few of her past purchases on our mac using her Apple ID I have to wait 90 days before I can do the same.
UNIX and by extension OSX is more than capable of handling multiple users, however the same cannot be said for iTunes and its Cloud-based service. It sees a Mac or PC as one device, regardless of how many users have their own accounts on it.
Sadly, my wife has downloaded past purchases on our Mac and I have to wait around 70 days before I can use Match or download any past purchases.
My advice would be to pick one main Apple ID to use with iTunes (such as the one you use with your Apple TV – if you have one) and then have any other member of the household transfer any music bought on an iOS device to the computer through the normal syncing process.
This is very, very, very annoying. I have no doubt that this is a limitation that has been imposed by the record labels and yes iCloud could provide an opportunity for pirates to get their hands on some free music, but once again it is the legitimate users who suffer.
Here’s a relevant forum conversation.
It appears that if you sign up for iTunes Match and your Mac has been assigned to an Apple ID other than your own, you can transfer it back to you during the subscription process. I have now reclaimed my iMac from my wife and am having my music collection matched to the Cloud.
Even so, limiting the service to just one user on a Mac or PC is simply idiotic.