What's the current state of Exchange-as-a-cloud-service? Just randomly Googling, it seems that RackSpace offers Exchange for $10/user. Something like that lets them keep the same look and feel, only a failure of the box in the basement isn't an instant catastrophe.
It's a consideration. Part of the impetus for this project is the fact that Exchange 2003 can't support anything past Outlook 2007 (as I've discussed on this forum here recently), so this is the biggest concern. These cloud services should be completely compatible with any of the new software that comes out, and if they're completely wedded to MS products, 365 can get them full installs on all their computers of the latest versions.
I suppose if I were building a clean-slate small legal office, I'd put them on Google Apps with a decently fast Internet connection and a consumer-grade router. I'd be tempted to get them a cheap file server as well, something with RAID5...
That's exactly what I'd like to do. They'll be doing digital file management, so they should have a local place to store scans from their new copier. Though, the models they're looking at can do cloud storage...