I recently heard from a Microsoft Mac beta tester that Microsoft's Exchange program is NOT planning on EVER releasing Exchange for OSX. What the hell is up with that? OSX has far superior networking capabilities to OSX Server, which I think they are doing... or maybe it was OS9... Either way, Microsoft's Exchange people need to get on the ball.
Trelane, I think you're confused about Exchange on the Mac.. at least, you're confusing ME! ;-)

The MS Exchange server does not now, nor it likely to EVER run on a Mac, OS X, OS X Server, OS 9, or otherwise. It's an NT/2000 based server app.

On the other hand, the MS Exchange CLIENT for Mac, currently known as Outlook Mac for Exchange server, does run under the Classic environment in OS X, and under Os 9 and below.

Further, MS is working on a new release of Outlook for the Mac, known by the code name "Watson." The new software, in beta now, offers full Outlook2000 for Windows compatibility when it comes to workgroup functions, such as group calendaring, task management, etc. It also looks significantly more like a true MAc app and not just another crappy Windows port.

What you may have heard from the beta user is this: "Watson" is not Carbonized. When it ships (maybe this coming winter), it will still be a "Classic" app. The group at MS responsible for Watson have stated that their FIRST priority was cross-platform compatibility (Mac to Windows). In future releases, they will quite likely Carbonize the Outlook client, which follows the same development strategy that the MS Mac Business Unit has in place for Office for Mac. I would be mighty surprised to ever see a Cocoa version of anything from Microsoft, but Carbonizing will probably come along within a year or so.

Hope that clears things up.