I have been running this setup for a few years now and it's great. I used to have a problem with GMail rejecting a lot of forwarded emails as spam but I set up graylisting (http://postgrey.schweikert.ch/) and since then I haven't had a single email rejected. It probably also matters how long you've been running your server so I would expect (assuming you're not actually sending or forwarding spam) to see the number of rejected emails decrease over time.

I ran a setup like this for several years but rejected/spam foldered emails were always a pain, plus a well-appointed mail host uses a fair bit of memory. I use Google mail now. It's not very expensive, and instant unconditional delivery to other Google mail users is a pretty nice perk. The nicest thing is not having the worry in the back of your head that just maybe something has gone awry with your setup and you are losing mail right now.