Optical is mostly reliable, however, they do occasionally suffer some problems. Sometimes, no matter how often you try, you cannot get a disk to mount although the agency who supplied it can still access the disk. This is usually down to different drives being slightly mis-aligned. Try formatting the disk and giving this to the design agency. They should be able to copy the files onto the disk and you should be able to read the disk.
Some disks can misread information.
Under certain circumstances Optical drives can misread information on the disk - especially with scans. There is no initial indication that the scan is wrong until you go to print when the RIP either bombs out or the print comes out with noise through it. To get round this always open every scan copied off an optical drive - this way you will detect any problems before they are printed. Lacie have also released a new version of Silverlining which will improve the drives performance. Optical disks are slow and the cost a per megabyte makes them unsuitable for archiving, however, as a transfer disk between design agencies and bureau's they are ideal.