Concur
I work a regular job and part of that involved dealing with Exchange. It requires some maintenance, but the really hard thing is fixing it when it breaks. It normally takes hours, and even the better part of a day. "On the side" I've also had a hobby server, and that runs qmail and vpopmail; basically a typical Unix mail server. This also requires maintenance, but the main difference is, with some average sysadmin and scripting skills, you can fix most problems so they stop happening (or are managed).
Overall, I'd say the hobby server's taken a lot less work, has had decent uptime, and has moved as much mail as the Exchange server, and has had more accounts and forwarding addresses on it -- over a hundred on Unix compared to around 25 on Exchange. It even ran mailing lists with between 5 and 15,000 addresses. And this is qmail, which can be pretty arcane. Postfix and Exim4 appear to be easier to run. Zimbra is built on top of Postfix.
The main edge Exchange has is the calendaring.
