Not that I thought being owned by Opera was a bad thing, but now they're completely employee owned again:
http://blog.fastmail.fm/2013/09/25/exciting-news-fastmail-st...
So I have high hopes that they'll continue to improve all that core functionality goodness.
The CardDAV and CalDAV stuff has been around for ages in Cyrus, but it's always needed a lot of work. I'm happy that the FM team has decided to take it on, even in beta it's been working wonderfully for me.
I remember attempting to use KOLAB groupware, which was based on Cyrus, but instead of improving the crappy CalDAV functionality (at the time) of Cyrus, they simply saved all the calendar objects as messages in special folders. Not necessarily a bad thing, but then they made the unwise decision to store the calendar data in a binary blob inside the message, meaning that they couldn't leverage IMAP/Cyrus' native indexing. Which meant that every message in the calendar folder had to be fetched, downloaded and parsed by the client for every view. Ugh, what a disaster. It basically fell over on calendars with more than a couple dozen events on them.