Mac OS X 10.8 Mountain Lion - Testing
I have "Preview 1" installed and i've successfully tested it with Active Directory as a mobile account on a laptop as well as Open Directory with group Manager.
Active Directory - worked great. Bound the computer and logged in with an AD account and mounted my network share. Everything seems to be running smooth.
Open Directory - Bound it to OS X 10.7.3 Open Directory Server and worked great. Anything I adjust so far takes effect on the new 10.8 client.
iMessges - works great as well. As the OS is linked to my iCloud account I was able to iMessage anyone on my phone from iMessages on the laptop by using a persons mobile phone number of email address.
So far I'm impressed!.