Sync iPhone with both of my Macs?

I must be missing something here.... I've got a Mac Mini at home, on which I've activated my iPhone. I've also synced my music from the Mini to the iPhone. Now I've bought my new MacBook, and even though I've authorized it on the same iTunes account as my Mini, I'm not able to sync my iPhone without wiping it. This is a problem since I don't have the same contents on both computers. So if I'm on the road with the MacBook and I buy a new album from iTunes, It pretty much has to live on the computer forever, since I can't transfer it to the iPhone?

Really, what this is doing is effectively making iTunes useless to me on the MacBook. I can plug in the iPhone, but it really does nothing for me except charge the battery.

Is it Apple that's being retarded here or is it just me?

@Jeffk,
Is your iphone set up to manually manage you music and/or videos?
I had that Problem with my iPod and my iphone at first.
Open iTunes>Open your iPhone>Then Summary and down about
3/4 of the page you will need to check off-Manually manage Music and Videos.
Thats should do it and if it doesnt then i might be able to help you other wise.

ok jailbreak your iphone then get the iswitcher program. you will be apple to sync your phone to any computer

Well the iphone acts as a storage device for your music. So when you plug in your iPhone to the Macbook go to file under itunes , and select transfer purchases from iPhone. This should put the music on the Macbook now just click sync iPhone and check of the music or playlist you want .
This worked with my Macbook and my iMac

Hope this helps!