How does a family with multiple idevices and multiple laptops share music and digital movie copies?
Here's our setup:

Computers:


iMac x 1 (wife's primary computer &amp; used by the kids)
MacBook Air x 1 (my primary computer)
MacBook Pro x 1 (wife's)


iOS Devices:


iPhone 4 x 2 (wife's and mine)
iPhone 3G x 1 (Younger Daughter's, used in airplane mode)
iPod Touch x 1 (Older Daughter's)
iPad 2 x 1 (mine but can be used by all when it's at home)
Apple TV 1st Generation x 1 (used in kid's playroom)
Apple TV 2nd Generation x 1 (used in main living room)


The Setup:

We use one Apple ID for all iTunes purchases (music, videos, books &amp; apps) across all devices. Each user of an iOS device also has their own unique Apple ID used for iCloud.

The iMac is our main hub. All music and videos are stored on it. All iOS devices with the exception of any that are mine sync with the iMac. I maintain my own music on the MacBook Air that I manually manage (I will copy over items from the iMac that I want on to the Air and will copy over times that I have added to the Air back to the iMac - I believe that this can be automated with the use of Home Sharing when both computers are on the same network). All iOS devices that are mine sync with the my Air.

Music on the kids's and wife's iOS device are managed individually via syncing with the iMac. This goes for videos as well, however we usually only access videos when we are at home and therefor rely on the built-in Home Sharing ability of each iOS device to stream content from the iMac to the device. This is also how we use the 2nd gen Apple TV.

We have no iTunes setup on the MacBook Pro as my wife uses the Apple TV or her iPhone to listen to music and only uses the laptop for web browsing.

The 1st gen Apple TV has been jail broken and has had its hard drive upgraded. I manually copy over videos to it for the kids (only non-iTunes purchased videos).

More info on Home Sharing: http://www.apple.com/support/homesharing/getstarted/

On Merging Apple IDs:

This cannot be done: http://support.apple.com/kb/HE37 (5th question down).