I'm not already using Google Apps across the board of domains I have, I've been slowly moving away as the increase in spam emails getting through the filters have been increasing. It is good at what it does, but there are better tools.
I currently maintain emails from over 6 domains, of which organisations are not linked, and due to security, they are not commonly linked under a single Google apps account (I've never seen a very positive look for it with the way I do things).
With Exchange I've completely dismembered and decentralised the basic requirement for federated and linked domains. I've known for a while now that this is where Google Apps has been slowly going. It doesn't fit my needs. Heck, I have email boxes /accounts for very specific things, such as ticket responders, transient subscriptions etc. It could easily cause my payment to Google to skyrocket.