I've used (and continue to use) Fastmail for many years behind a personal domain.
To call Fastmail reliable is a bit of a laugh. They've had at least three severe outages in my time there (we're talking 24+ hours without mail access). To their credit, nothing was lost in the end, however I was fuming by the end of the last one and determined to switch to Gmail. However inertia has kept me from doing so -- last time I checked it was tricky in Gmail to import a complicated set of folders like I have and retain the structure, so it's always been something I plan to get around to once I have time. Yeah right.
FWIW, I don't think there's been a significant outage since the Opera purchase. And I'm quite pleased with what I've seen of FM's beta interface.