Apple’s Snow Leopard release date won’t be until September, but you can preorder the upgrade for just $29 right now, exclusively from Amazon.com.
The new Snow Leopard operating system is said to use just half the footprint of previous versions, with improvements to Stacks, Exposé, and Time Machine backup.
The list of Snow Leopard changes and improvements at Wikipedia also notes support for Microsoft Exchange:
Mac OS X Snow Leopard will include out-of-the-box support for connecting to Microsoft Exchange 2007 servers for access through Mail, Address Book, and iCal. This will make Mac OS X systems the first to be bundled with Microsoft Exchange 2007 support across the range, as Microsoft Windows require the purchase of Microsoft Office Outlook.