I'm sure we all remember the colourful discussion on Exchange and open source alternatives (start here for my final post on the topic) that took place between myself and Alex Scoble just a few weeks back.

Lots of interesting comments, from both sides, came out from that discussion, and like all good debates there were no real winners.

Now, there's another active conversation (I use the term loosely) on the topic taking place on Slashdot after the release of the Zimbra Collaboration Suite. Inevitably some of the same topics are coming up - including the down, and up, sides of Exchange's data model, hardware requirements and flexibility. All of them come with fiarly good comments on observations from both sides of the fence.