Eh... I have had some problems in the past when trying to copy many files from one drive to another. Assuming you're making basically a duplicate of a drive, have you looked into software that does this? Typically the drive manufacturer offers such software for free.
I back up 100s of gigs at a time with rysnc via shell scripts all the time, so no its not bad at all. It gets bad in unstable environments, and never ever cut and paste, copy and paste first, then go back and over write data.
yeah i think 340 gig i moved! it was fine just took ages and also when i was doing it it was from 1 drive to an identical one! dont know if that makes any sort of difference?