Fastmail.fm has been around quite a while, and while I still would consider them a success, I don't think they have done much in the form of innovation. Most of the innovation I have seen in email for the year, has been in the form of the client, not the server.
From what I have read on the fastmail.fm blog, etc, they tend to do some very good stuff on the back-end, particularly(open source) contributions to the Cyrus IMAP server. These, I understand, have improved the failover and resilience of the IMAP server a lot. These might not be "innovations" in a technical sense, but they certainly make Cyrus a much better server for Enterprise users.
The less said about fastmail.fm's "innovations" on their web interface the better.
