Server side encryption is a showstopper. Most people have learned from the example of Hushmail. Not everyone, of course. You would get some users, but not many. An open source browser plugin that can be audited and works with locally stored keys is much safer. Why don't you talk to SelfSovereignty about his project, MetaSilk. He is planning on adding PGP support to it and could use some help. http://dkn255hz262ypmii.onion/index.php?topic=121039.0