I've only sequenced a few samples on a MinION. The dominant error seemed to be miscounting the length of a homopolymer stretch (e.g. CCC->CCCCC) but the substitution error rate was also clearly worse than Illumina. I've gotten used to less than 0.1% error from DNA sequencing on a HiSeq 2500. My guess is that the MinION data had 1-3% substitution errors.