This was an interesting read:
Photokina 2012: Interview - Stephan Schulz of Leica : Digital Photography Review
Note the comments about the D800.
Q; Do you feel any pressure from cameras like Nikon's D800, which offer comparable pixel counts to the S?
A; Many people ask me this question, but people who really like to work with medium format don't ask me that...This question comes only from people who have no experience of medium format at all.