[DyslexicAtheist]

When it comes to criticism about backup I have no problems with things getting wiped from the server. I assume a good p2p design has a "little server" and as much client as possible in it.

Enforcing in the clients to properly back up by default, or otherwise properly educating the user of what happens if they don't back-up would be as important as getting the code right. There is little difference to the user whether they lost data because they didn't understand they really had to do backups, or they got their keys compromised and messages deleted by a malicious 3rd party.

I do agree with all of GP's other points though.