Ok, we know the Exchange 2010 HA design is more flexable, and has a lot of new features.
But we have now "tested" it in live inveronment.
Consider this scenario:
4 mailbox servers i 2 DAG's
One dag, contains a server in London, and a server in Denmark(datacenter)
The other dag contains a server in newcastle, and a server in Denmark(datacenter)
All part of the same exchange org.
Well we had to move 20 users from newcastle to London.
Because this can be done as a online move in E2010, we did it in the middle of the day - shouldn't cause a problem...
But then the mailserver in newcastle went down because a technician accidentally unplugged the power cord ...
The users failed over to the mailbox server in Denmark, without noticing.
After powering the mailbox server in Newcastle up again, we set the Newcastle database as active again.
After that, the online mailbox move resumed, and finished.
The users didn't barely notice at all :-)
I thought that was pretty cool.