Hang in there, I went through this process not long ago and only had around 100 gigs to sync and it took at least 24hrs.
Trust me on this, it will work but depending on how much data it has to sync back it could take up to 72hrs. You may notice the time left jumping all over the place, But then as it gets closer to being done it will display say about 200 - 300 mins and then it will count down consisitently from there.
Whatever you do, don't hit cancel, call tech support, etc. Like I said I went down the exact same path back in feb 2011 and made all the mistakes of trying to cancel it, shut it down, etc and the whole time it was doing it's thing I just wasn't patient. Again, DO NOT call tech support as this will only frustrate the s*** out of you and you will get varying advice and several different stories.
I finally after a few calls to support insisted I speak to a higher level support specialist who knew his s*** and he said just leave it go and it will work, just very slowly.
So, I did what he said and then finally I just left it for a day or so and voila it finally worked.