In my experience Mozy does not easily handle that amount of data. I did in the end (after many, many months) get it to finish the initial backup of my 100GB of data.

However, it really struggle with the daily incremental backups. It can take hours for it to do the initial scan to work out what needs backing up. It then can take ages to backup a few megs of a multi gig file that has just changed a little (a great example of this is Virtual PC drive images). It often doesn't complete a days changes within the 10 hours or so I can let it run at full speed each day.

So great in theory, in practice my home made rsync backup still works much more reliably. Still, at least it works better than Carbonite...