How can I share apps and music purchased on one apple ID between 7 devices?

I have:

• 1 Macbook Pro for office use
• 1 Macbook Air for personal travel use
• 1 Mac Mini to run my home theater system
• 1 iMac that my wife and kids use
• 1 iPad v1 for the kids to play with
• 1 iPad v2 for myself
• 1 iPhone 3GS

I'm running into problems with iTunes telling me I've authorized too many devices. I have seen in some places people saying that I'm allowed to authorized up to 10 devices, 5 of which can be computers, but iTunes seems to be treating computers and other devices the same for me, limiting me to 5 no matter what.

Any ideas what might be wrong?

Maybe you have authorized Macs you no longer have.

Go to your account in iTunes, under Apple ID Overview you can see how many computers you have authorized and (once a year) you can deauthorize all, after that you should be able to reauthorize your Macs. (This does not affect iOS devices, as they do not count towards your 5 devices limit)