I have discovered your project today and i find it very interesting. However, I do feel that the compatibilities you announced are lacking one major player : Lotus Notes. There are more than 100'000'000 Notes users and I believe that not addressing this user group will make the project less interesting.
Or is there something I have failed to read ?
We understand that Lotus is a top client in the enterprise. Can you tell us about what version you are using. Do you feel that it would be enough to use Notes with IMAP to access our system? Can you tell us more about what you think would be the right integration for Notes.
The notes client may access imap or pop 3 mail. It includes a calendaring/scheduling application and ICAL standards are upheld.
However, I do think the issue must be considered the other way around. 118 million Notes users mean millions of Notes/Domino mail servers. Your mail client ought to be able to access a mailbox on a notes server. The same way your calendaring features ought to be able to work with a Notes/Domino server.
One last thing for people who are interested. Lotus supplies its mail and calendaring applications with accessible source code. This is not open source in the official sense, but you may program new features, change things in the mail/calendar applications if you wish as well as learn how they did it.