At first, I was pretty ticked at Apple too for not comming up with a solution.
I'm not mad at them anymore because I now realize that they have given us the best that the movie/music industry will allow.
Apple has agreed to tie each purchace to one email address for copyright reasons.
You can change the email address of any Apple ID to an email address that is not already an Apple ID and not a me.com address; however, if you do change it, you may need to re-download all purchases for that account to make all purchases properly and consistantly associate with that new primary Apple ID email address.
Now here is a solution for those of you who made purchases from different Apple IDs.
1. Pick the Apple ID that you have made most if not all of your Movie & App purchases with and make it your primary Apple ID/Acount that you make all new purchases with.
2. Create an AAC version of your music purchases from your other Apple ID's. This may in and of itself strip the DRM copy protection from it, but if not, you may need to take the extra steps of burning it to a disk (re-writeable) and then ripping it back to the MAC. Then it will play when signed into any Apple ID or none at all. Be sure to set your write and rip settings in iTunes appropriately. [For the best quality music you may even choose to upload your lower quality music up to iTunes Match and then down load from iTunes Match a better quality copy DRM free.
This should get most, if not all of your iTunes library under one Apple ID.
An Apple representative told me that the same can be done with movies to get them to play reguardless of which account is signed in; however, it can only be redownloaded from it's original Apple ID as you might expect. Good luck burning and ripping a high def movie however. Not saying it can't be done, it you've got the right equiptment, but goodluck.
What I hate is that I cannot take my Apple ID's Alternate email address (which is a me.com address necessary for iCloud's Mail and permantly linked to that Apple ID) and make it the Apple ID's primary email address. Apple's reason to disallow this appears to be that Apple....
1. wants us to by billed for iTunes at a non-me.com address so that they can still reach us if they decide to disable our Apple ID/iCloud account for any reason.
2. perhaps wants to avoid explaining their customers how to redownload all purchases which seems techie, cumbersome, unsmooth (and therefore un-Apple).