quote:
"It didn't allow single sign-on service, user migration and couldn't help us centrally manage multiple domains."
I call FUD. Google Apps has SSO:
http://www.google.com/support/a/bin/answer.py?hl=en&answer=60224
https://www.google.com/support/a/bin/answer.py?hl=en&answer=174917
Google Apps has user migration (and unlike MS, they make it easy to migrate your data OFF Google Apps:
IMAP Based: http://www.google.com/support/a/bin/answer.py?hl=en&answer=61369
http://www.google.com/support/a/bin/answer.py?hl=en&answer=61369
Exchange Based: https://www.google.com/support/a/bin/answer.py?hl=en&answer=172212
https://www.google.com/support/a/bin/answer.py?hl=en&answer=172212
Moving off Google Apps: http://www.dataliberation.org/
http://www.dataliberation.org/
centrally managed domains is the only issue mentioned that's really an issue. Multidomain support is present but not as flexible as Exchange is. This is more an inconvience though as the IT Department can just manage the domains seperately if need be.