Microsoft's finally taken the lid off a very, very cool addition to their product line: the Feature Pack for Windows Storage Server allows you to put your Exchange 2003 databases on a Windows Storage Server NAS box. There are some limitations: this approach is designed to handle up to 1500 concurrent users, and it requires good network connectivity between the Exchange server and the Windows Storage Server. However, it's a real, live, supported-by-PSS solution that can potentially deliver SAN-scale performance to organizations that can't afford Fibre Channel SANs. Check it out.