Here's a tip that may save you a 16 gig download through origin (or at least it is a good way to get a copy of all the updates and patches).
I stuffed up my BF3 installation today, don't ask how (d'oh). So I tried to do a repair and origin just wanted to download the whole 16 gigs worth, not even looking at my installation disks. The normal system restore wouldn't restore the BF3 folder. Eventually I chanced upon the restore a folder to a previous version option, by right clicking the damaged BF3 folder. It allowed me to save a copy of the whole 16 gig BF3 folder, a good version from 1 hour ago, or even 1 month ago, and save it to a different location. I saved it to a different HDD. I then deleted the stuffed folder, and copied the good one back to where it belongs. Its all working perfectly, and now I have a whole backup copy of the BF3 folder. If the method hadn't of worked perefecty, at least BF3 would be all there, and you can use origin to do minor repairs to the installation.