Just got out from 3 day engagement with one of the top Canadian Exchange guys. I leaned a lot about exchange 2010. One of the big changes that they are talking about is the shift away from SAN storage, back to local storage.
2010 is using DAG, which allows store replication, and redundant mailbox servers. The store information is moved out of the server settings in AD and moved up to the exchange org level, so that you can have multiple stores that replicate across active directory sites, and therefore geographic locations.
The exchange guy went as far to say that, given three mailbox servers in one geographic location, you could install the mailboxes on raid0 or jbod. If you had four servers split into two geographic locations, not only could you use jbod, but you would forgo the need for backups.
The caveats to all of this are that you require Windows Server Enterprise per backend server. If you want to have a full hot site, the server requirements go up exponentially, especially if you require full functionality, like OWA across the two sites, since at that point you can't use NLB and have to go to hardware load balancers.
To do a full redundant hot site with no single point of failure and full functionality, you require twelve servers, and 8 hardware load balancers. You don't need a SAN, but at that point, you might wish that's all you needed.