We use Mimecast now which is great, but seems to be a bit of overkill for what we're doing, which also makes it more difficult to manage than it needs to be.
I've heard a few people mention MBS, Inc. and their hosted Barracuda service and was just curious what your experience with that has been.
We LOVED pre-Google Postini but it got progressively worse over time and then Google switched us to Google Apps ahead of schedule and gave admin rights to an ex-employee who had tried signing us up for Google Apps outside of IT, so we were forced to switch.
Mimecast has been great but a little cumbersome for the margin I have with regards to spam filtering.
We're hosted Exchange for now, but will be moving mailboxes to O365 this year if at all possible.