I have messed with running my own email server from time to time, but it generally takes about a day before I get an email bounced back thanks to the overzealous IP blacklists--for instance, as I recall, all Comcast dynamic IPs are blocked automatically by Spamhaus. Great, so I either need to pay extra for a static IP which might be non-blacklisted, or I can pay for hosting and just hope that's not blacklisted. Gmail is big enough and rich enough to stay off the blacklists, I'm not. So I use Google Apps hosting, even though I'd rather not.