By unsupported, we mean that you WILL encounter problems that havn't been solved. You may be able to get things working by "tweaking" it a little, but when an update comes out, you will likely face additional problems.
I run CentOS. It has been extreamly stable with updates, etc. The only reason I use CentOS is because we're poor
Although CentOS isn't supported by Zimbra, it's Binaries are made to be compatable with RHEL.
Just to be clear, I am not endorsing CentOS as an alternative to RHEL, I'm simply saying that it should work.
We just bought some macintels, and we're gonna migrate to that.
OSX ROCKS!