I've been using it for several months now. I really like it. It's fast, and reliable. I made the move, and haven't (really) looked back.
The spam filtering isn't as good though. I've had a few false positives and false negatives. I don't get much spam, so it's not hard to have a quick look in the spam folder. Wish I didn't have to do this though.
I like paying for the product. It's nice to know my emails aren't being scanned to build up a profile on me. It's nice to know that I am a customer (of the traditional kind). I haven't had to use support yet, but it's there. Unlike Gmail.
I originally moved because I grew uneasy with the amount of information I had with Google. Now, I have none. A small win for me, but Google doesn't care. Ultimately, make the decision on the whole "best tool for the job" argument.
I've been using it for months. It seems like a serviceable IMAP backend. The spam filtering lets me down but anything is better than getting sucked back into Google again.
I would hope it's servicable! I put a lot of work into making it robust. It helps that we talk IMAP to the backend servers as well rather than some custom protocol (OK, so there are some IMAP extensions we use in house as well - but they're very much in the spirit of regular IMAP)
