How can I backup my apps from the iPad to my mac?
First, you should authorize your computer with your iPad if you haven't already. 


From the Store menu, choose Authorize Computer.
In the dialog that appears, the Apple ID button is selected by default. If you have an  AOL account, select AOL.
Enter your Apple ID or AOL screen name and password, then click the Authorize button.


Then, transfer your purchases: 

From the File menu, choose "Transfer Purchases from "Lipis' iPad" "

Wait for iTunes to complete the transfer. 

Check in your library for your apps and the like.

Then you can sync without worry.