I recently upgraded a 2GB database from 6.5 to 7.0 using one computer. I requested the byte-by-byte comparison. The upgrade proceeded smoothly and no errors were reported. However, when we checked the data we found these problems:

1. for some tables, not all rows were exported. For example, had 1572 records in the 6.5 database but only 1474 were exported.
2.floating point values for some numbers became approximations. For example, 15.0 became 14.9999999 while 17.0 became 17.0000001. (Reminds me of the floating point problems with with the early Pentiums.)