The experience has been as I expected it would be: quite painful. We have not gone an entire month without service disruption. There have been problems with the service getting blacklisted. Support is, well, Microsoft support -- untimely, disconnected, uncaring, and when phones are involved very difficult to understand.
Anecdotal, sure, but according to the various forum/community postings I've come across trying to resolve various issues, not uncommon.
Caveat emptor.
edit: turns out what I was talking about (office365) and what the OP is talking about (outlook.com) aren't the same thing. Apologies.