Well crap. We use different Apple IDs on our Macs now. When we had the 3G a long time ago we used different Apple IDs because of the contacts. I'd love to use the same Apple ID but I'd be afraid of us messing up each other's contacts.
It may be alright if you sync through iTunes with one device, transfer your purchases to the mac; and then sync the other device, and install the apps. IN fact, I am pretty darn sure it will be -- except for stuff that is password-controlled through specific accounts. I.e., I subscribe to the Daily, $40 per year. My wife can read it on her iPad, because she is using my Apple ID. If she had her own, the subscription would NOT work.