For what it is worth I am running 6.0R3.1 Previously I was on 5.5R4 which I found to be pretty stable. Whenever I first upgraded to one of the first 6.0 releases it was pretty bad; however, I've found that 6.0R3.1 fixed most of my issues. I had an issue previously with the SSO into OWA and that was fixed, sharepoint 2007 was supported, and the Outlook Meeting plugin is working in 6.0R3.1. All of which were things I had issues with in the previous releases.
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