since u have nero 7 you can use its in built disc quality testing program called "nero cd-dvd speed". using the disc quality scan you can see the number of pi (parity inner) errors, pi failures, po (parity outer) failures and the jitter. the program will give the disc a score out of 100 and this should be taken only as a rough guide on the quality of the burn
basically any disc with a po error is an automatic failure. according to the ECMA's standards the pi error peak should not be more than 280 and the pi failure peak should be lower than 4. not sure about what the standards say about the rest.
you should always aim for the lowest possible amount of errors, especially for storage. though not to say that discs that have error rates higher than the standards neccessarily mean that the disc is a dud. it just means there is a higher likelyhood of the disc not working with every drive.