May I offer an alternative back up strategy? Get an external HDD, and use SuperDuper!, or Carbon Copy Cloner, or another cloning backup application to create a bootable clone of the MBP.
If and when the MBP breaks you can plug the external HDD into the iMac, and boot from the external HDD. Functionally, this is the same as swapping the HDD from your MBP into the iMac. The MBP programs, desktop, settings, etc are all available on the iMac. (Nothing on the iMac, however, is disturbed or changed). You can keep working away on whatever projects you had on the MBP while it is in the shop. When it comes back you simply clone the external HDD back onto the MBP and carry on.
A couple of things to note though are... the external HDD should have a fast connection - USB 2 works fine for the nightly backup... but you'll pull your hair out booting from it and using it if you have to boot from it. I've got FW800, and it's OK to use. In my case I used by MBP as the backup computer for a dead Mac Pro.
Not all applications will work off the shelf. For instance, iirc, my accounting program looks for a particular hardware combination before it will start up. So, test your backup and make sure your core applications will work. And if not, how do you get them working quickly.
Good Luck.
