A little off topic, but Mike - have you ever looked at PostPath (recently acquired by Cisco)?
The last implementation I did involved 4 standard Microsoft DC's, but all the mailboxes were stored on PP servers. The organisation had 50,000+ users and slashed their CAL bill by 65%. None of the clients know any different, and mailbox backup was simplified enormously.
Just a thought if you wanted to double your profit margin.