In order to determine the accuracy of the genome profile provided by 23andMe and deCODEme I arranged to be genotyped by both companies and wrote a computer program to compare the results.
The downloaded files contains 576105 snips in the case of 23andMe and 1013349 snips for deCODE. After removing the no-call and matching the two files by SNP identification, 560299 snips were present in both files. The comparisson revealed 23 cases in which the results do not agree. See the results here.
This error rate seems to me to be quite acceptable and I wonder if this is the rate expected in scientific studies using the same technology.