Transfer your iTunes library, which includes your app and music purchases from the PC directly to your new MacBook Pro. Your photos, contacts, and other information can be transferred also if you use Migration Assistant.
This explains how to use Migration Assistant: OS X Lion: About Windows Migration Assistant
After you sync the iPhone to the PC for the last time, "deauthorize" the PC for music purchases.
When you sync the iPhone to the MacBook for the first time, it will tell you that it is already synced to another computer, and give you the option to erase and sync it to the MacBook.
I have a similar issue. I have not synced my iPhone 4 to my PC in months - I have been updating apps on the phone itself and backing up to iCloud. I now have a MacBook and have not connected the iPhone 4 to it at all.
Now today, I purchased an iPhone 5. I installed the iCloud backup, but of course that didn't include my apps or my photos that were taken longer than 30 days ago. I'd like to have both my apps and my photos on my new phone.
Do I need to sync my iPhone 4 with my PC one last time, transfer that info over to my MacBook, and then somehow install that backup onto my new phone? I have some music on the iPhone 4, but do not care if that is lost in the transfer process. Also, on iTunes on my PC, all the music is stored on external HDs, and almost none of it is purchased from iTunes.